HK1094101A - Soft handoff with interference cancellation in a wireless frequency hopping communication system - Google Patents

Description

Soft handoff using interference cancellation in a wireless frequency hopping communication system

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to the following applications, all assigned to the assignee of the present application:

filed on 12.5.2003, entitled "Soft Handoff with interference cancellation in a Wireless Frequency hosting Communication System", co-pending U.S. application No. 06/470160.

Technical Field

The present invention relates to communications, and more particularly, to a technique for supporting soft handover with interference cancellation in a wireless frequency hopping communication system.

Technical Field

In frequency hopping communication systems, data is transmitted on different sub-bands in different time intervals, referred to as "frequency hopping periods". These subbands may be provided by Orthogonal Frequency Division Multiplexing (OFDM), other multicarrier modulation techniques, or some other concept. With frequency hopping, data transmission hops between subbands in a pseudo-random manner. Such hopping provides frequency diversity and enables the data transmission to better withstand deleterious path effects such as narrowband interference, jamming, fading, etc.

Orthogonal Frequency Division Multiple Access (OFDMA) systems use OFDM and can support multiple users simultaneously. For a frequency hopping OFDMA system, a particular user's data transmission may be sent on a "traffic" channel associated with one particular Frequency Hopping (FH) sequence. The FH sequence indicates the particular subband to use for data transmission in each hop period. Multiple data transmissions for multiple users may be sent simultaneously on multiple traffic channels associated with different FH sequences. These FH sequences may be defined to be orthogonal to each other so that only one traffic channel, and therefore only one data transmission, uses each subband in each hop period. By using orthogonal FH sequences, multiple data transmissions do not interfere with each other, while enjoying the benefits of frequency diversity.

An OFDMA system may be deployed with multiple cells, where a cell generally refers to a coverage area of a base station. A data transmission on a particular subband in one cell is interference to another data transmission on the same subband in a neighboring cell. To randomize inter-cell interference, the FH sequences for each cell are typically defined to be pseudo-random with respect to the FH sequences of neighboring cells. Interference diversity is achieved by using pseudo-random FH sequences for different cells, and the data transmission of one user in one cell observes an average interference from the data transmissions of other users in other cells.

In a multi-cell OFDMA system, it is very good to support "soft handover". In the soft handover process, a user communicates using multiple base stations simultaneously. Soft handoff may provide spatial diversity to prevent deleterious path effects via data transmission to or from multiple base stations at different locations. However, when the system employs frequency hopping, soft handoff is complicated. This is because, in order to randomize inter-cell interference, the FH sequences for one cell are pseudo-random (i.e., non-orthogonal) with respect to the FH sequences of neighboring cells. A given base station of the multiple base stations may instruct users using the multiple base stations for soft handoff to use the FH sequence. The data transmission sent by the soft handover user is orthogonal to the data transmission sent by other users of the designated base station, but pseudo-random with respect to the data transmission sent by users of other base stations. The soft handover user will cause interference to users of other base stations and will therefore also receive interference from these users. Interference degrades the performance of all interfered users unless it is degraded in some way.

Accordingly, there is a need in the art for techniques to support soft handoff in frequency hopping OFDMA systems.

Disclosure of Invention

Techniques are provided herein to support soft handoff in a wireless communication system (e.g., a frequency hopping OFDMA system). Each cell in the system may be divided into one or more sectors. Each sector in the system may simultaneously support a set of "no-handoff" users and a set of "soft-handoff" users. A non-handed-off user is a user that uses only one sector for communication (i.e., is not in soft handoff). A soft handoff user is a user that communicates using multiple sectors simultaneously.

For each sector, the sector assigns a traffic channel to each non-handoff user of the sector, and the "serving" or "host" sector of each soft handoff user assigns a traffic channel to the soft handoff user of the sector. The serving sector for the soft handoff user is a designated sector of a plurality of sectors used by the soft handoff user to communicate. For each sector, the traffic channels assigned to the non-handoff users of that sector are orthogonal to each other and may or may not be orthogonal to the traffic channels assigned to the soft handoff users of that sector, depending on whether the sector is the serving sector for these soft handoff users.

For each sector, the handoff-free users for that sector can be power controlled so that when there is interference from soft handoff users for that sector and interference from users of other sectors, that sector can receive and decode their data transmissions. Soft handoff users may also be power controlled so that their sectors are able to decode their data transmissions while reducing interference to non-handoff users.

Each sector processes its received signal and recovers data transmissions from handoff-free users of that sector. After decoding the data transmissions from the non-handoff users, each sector estimates the interference caused by the non-handoff users of that sector and cancels it from the received signal. Each sector also processes its interference-canceled signal to recover the data transmission from the soft handoff users of that sector.

Various aspects and embodiments of the invention are described in detail below.

Brief Description of Drawings

The features, nature, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly or similar elements or steps and wherein:

fig. 1 shows an OFDMA system;

fig. 2 illustrates frequency hopping of one sector in an OFDMA system;

fig. 3 is a block diagram of a terminal;

FIG. 4A is a block diagram of a base station in a synchronous system;

FIG. 4B is a block diagram of a base station in an asynchronous system;

FIG. 5 is a block diagram of a Receive (RX) data processor within a base station in a synchronous system;

FIG. 6 is a block diagram of an interference estimator and interference canceller within the RX data processor;

FIG. 7 is a block diagram of an OFDM demodulator/RX data processor within a base station in an asynchronous system;

FIG. 8 is a block diagram of an interference estimator and interference canceller within an OFDM demodulator/RX data processor;

fig. 9 is a flowchart of a terminal transmitting data; and

fig. 10 is a flow chart of a base station receiving data transmissions from multiple terminals.

Detailed Description

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

Fig. 1 illustrates an exemplary OFDMA system 100 supporting multiple users. System 100 includes a plurality of base stations 110 that provide communication with a plurality of terminals 120. A base station is a fixed station used for communicating with the terminals and may also be referred to as an access point, a node B, or some other terminology. Terminals 120 are typically dispersed throughout the system, and each terminal may be fixed or mobile. A terminal may also be referred to as a mobile station, User Equipment (UE), a wireless communication device, or by other terminology.

Each terminal may communicate with multiple base stations on the forward link and/or multiple base stations on the reverse link at any given moment. Depending on whether the terminal is active, whether soft handover is supported, and whether the terminal is in a soft handover state. The forward link (i.e., downlink) refers to the communication link from the base stations to the terminals, and the reverse link (i.e., uplink) refers to the communication link from the terminals to the base stations. In fig. 1, terminal 120c is in soft handoff with base stations 110a, 110b, and 110c on the reverse link, terminal 120d is in soft handoff with base stations 110a and 110c, and terminal 120g is in soft handoff with base stations 110b and 110 c. The remaining terminals are not in soft handoff. For simplicity, fig. 1 does not show forward link transmission.

System controller 130 is coupled to base stations 110 and may perform a variety of functions, such as: (1) coordinating and controlling base stations 110; (2) routing data between the base stations; and (3) access and control of terminals served by these base stations.

Each base station 110 provides coverage for a respective geographic area 102. The term "cell" can refer to a base station and/or its coverage area depending on the context in which the term is used. To increase capacity, the coverage area of each base station may be divided into multiple sectors (e.g., three sectors 104a, 104b, and 104 c). Each sector is served by a corresponding Base Transceiver Subsystem (BTS). The term "sector" can refer to a BTS and/or its coverage area depending on the context in which the term is used. For a sectorized cell, the base station for that cell typically includes the BTSs for all sectors of that cell. The following description assumes that each cell is divided into a plurality of sectors. For simplicity, in the following description, the term "base station" refers generally to a fixed station that serves a cell and a fixed station that serves a sector. The base stations of all sectors of the same cell are typically implemented within one physical base station of the cell.

The techniques described herein may be used to support soft handover in which a terminal communicates using multiple cells simultaneously. The base stations of these cells are included in the active set (activeset) of the terminal. These techniques may also be used to support "softer handoff" in which a terminal communicates using multiple sectors of the same cell at the same time. The base stations for these sectors (typically portions of the same physical base station) are included in the active set for the terminal. For simplicity, in the following description, the term "soft handover" generally refers to a case where a terminal communicates using multiple cells at the same time and a case where a terminal communicates using multiple sectors of the same cell at the same time.

The techniques described herein may be used for a synchronous system in which the times of multiple base stations in the system are synchronized to a common clock source (e.g., GPS). These techniques may also be used in asynchronous systems where the times of multiple base stations are not synchronized. For clarity, it is assumed that the primary user (defined below) of each sector is synchronized with the base station of that sector.

OFDMA system 100 effectively partitions the overall system bandwidth into multiple (N) orthogonal subbands using OFD M modulation techniques, where N > 1 and is typically a power of 2. These subbands are also commonly referred to as audio (tone), subcarriers, bins (bin), and frequency subchannels. With OFDM, each subband is associated with a respective subcarrier that may be modulated with data. In some OFDM systems, only N is present_DSeveral sub-bands for data transmission, N_PSubbands for pilot transmission, N_GUnused sub-bands are used as guard sub-bands to make the system meet the requirement of spectral mask (spectral mask), where N is N_D+N_P+N_G. For simplicity, the following description assumes that all N subbands are available for data transmission.

Fig. 2 illustrates frequency hopping of one sector in an OFDMA system. As described above, various benefits may be obtained using frequency hopping, including frequency diversity and interference randomization to combat deleterious path effects. In this example, N is 8, and numbers assigned to the 8 subbands are 1 to 8. Up to 8 traffic channels may be defined, where each channel uses one of the 8 subbands in each hop period. A hop period may be defined equal to the duration of one or more OFDM symbols.

Each traffic channel is associated with a different FH sequence. Can be based on the FH function f_s(k, T), the FH sequences for all traffic channels in the sector are generated, where k represents the traffic channel number or Identifier (ID) and T represents the system time in units of hop periods. By FH function f_sIn (k, T)N different FH sequences may be generated for N different values of k. The FH sequence for each traffic channel indicates a particular subband to use for that traffic channel in each hop period.

Fig. 2 shows the subbands for two traffic channels 1 and 4. The FH sequences and subbands for traffic channel 1 are indicated by the black squares, while the FH sequences and subbands for traffic channel 4 are indicated by the slashed squares. As can be seen from fig. 2, each traffic channel dynamically hops between sub-bands in a pseudo-random manner determined by its FH sequence. In this example, the FH sequence f of the traffic channel 4_s(4, T) is the FH sequence f of traffic channel 1_s(1, T) vertical motion variants. The sub-band used by traffic channel 4 is related to the sub-band used by traffic channel 1 as follows:

f_s(4，T)＝(f_s(1，T)+3)mod N。

to avoid intra-sector interference, each sector may use an orthogonal FH sequence for its traffic channel. FH sequences are orthogonal to each other if no two FH sequences use the same subband in any hop period T. This orthogonality condition is achieved by defining the FH sequences for each sector as vertically shifted versions of each other, as shown in fig. 2. Thus, the traffic channels of each sector are orthogonal to each other because they are associated with orthogonal FH sequences. Because each subband can only be used by one traffic channel in each hop period, interference between multiple data transmissions sent on multiple traffic channels in the same sector is avoided.

For a multi-sector OFDMA system, data transmissions for users in one sector can interfere with data transmissions for users in other sectors. To randomize inter-sector interference, different pseudo-random FH functions may be used for different sectors. For example, sector s may be divided₁FH function f_s1(k, T) is defined relative to sector s₂FH function f_s2(k, T) is pseudo-random. In this case, sector s₁The FH sequence for traffic channel k will be pseudo-random with respect to the FH sequence for sector 2 for traffic channel m, where k may be equal to or greater thanIs not equal to m. When "collisions" occur between the FH sequences of these traffic channels, i.e., when f_s1(k，T)＝f_s2(m, T) and traffic channels k and m use the same subband in the same hopping period, interference occurs between traffic channels k and m. However, due to the FH function f_s1(k, T) and f_s2The pseudo-random nature of (m, T), the interference will be randomized.

Thus, the FH sequence for each sector can be defined as:

1. orthogonal to each other to avoid intra-sector interference; and

2. the FH sequences for adjacent sectors are pseudo-random to avoid inter-sector interference.

With the above constraints, a user assigned a traffic channel k by a sector is orthogonal to all other users assigned other traffic channels by the sector. However, this user is not orthogonal to all users in adjacent sectors that use different FH functions.

Referring back to fig. 1, each sector supports both a set of non-handed-off users and a set of soft-handed-off users. Each user may communicate with one or more sectors depending on whether the user is in a soft handoff state. The sectors used by the users for simultaneous communications are included in the "active set". For a handoff-free user, the active set includes a single sector, i.e., the user's serving sector. For soft handoff users, the active set includes a plurality of sectors, one of which (e.g., the strongest receiving sector) is designated as the serving sector for the soft handoff user.

Each sector assigns traffic channels with orthogonal FH sequences to handoff-free users of that sector, and therefore, the users do not interfere with each other. The serving sector of each soft handoff user assigns a traffic channel to that user. Each soft handoff user is orthogonal to the other users in its serving sector and therefore does not interfere with each other. However, each soft handoff user is not orthogonal to other users in other sectors in its active set. Thus, the soft handoff users for each sector may or may not interfere with handoff-free users for that sector. Depending on whether the sector or other sectors have allocated traffic channels for these soft handoff users.

For each sector, the non-handoff users for that sector can be power controlled so that the sector can decode their data transmissions if there is interference from the soft handoff users for that sector and interference from users of other sectors. Soft handoff users may also be power controlled so that the sectors in their active set are able to decode their data transmissions while reducing interference to non-handoff users.

In one embodiment, each sector processes its received signal and recovers data transmissions from handoff-free users of that sector. Each sector then estimates the interference caused by the non-handed-off users and cancels it from the received signal. Each sector further processes its interference-canceled signal to recover the data transmission from the soft handoff user for that sector.

Each sector can also be considered to support a set of "primary" users and a set of "secondary" users simultaneously. For each sector, a primary user is the user assigned a traffic channel by that sector, and a secondary user is the user assigned a traffic channel by any other sector. The primary users of each sector include: (1) non-handoff users of the sector; and (2) the serving sector is a soft handoff user for that sector. The secondary users for each sector include soft handoff users whose serving sector is other than the sector.

In another embodiment, each sector processes its received signal and recovers data transmission from primary users of the sector, including handoff-less users of the sector and soft handoff users assigned a traffic channel by the sector. Each sector then estimates the interference caused by these primary users and cancels the interference from the received signal. Each sector further processes its interference-canceled signal to recover data transmissions from secondary users of that sector (assigned traffic channels by other sectors).

Each sector may also recover data transmissions from users in other ways than the two embodiments described above, which also fall within the scope of the present invention. In general, it is desirable to cancel as much interference as possible. However, the ability to cancel the interference caused by a particular user depends on the ability to correctly decode the data transmission from that user, which depends on other factors such as the manner in which the user is power controlled.

Fig. 3 shows a block diagram of one embodiment of terminal 120x, terminal 120x being one terminal in OFDMA system 100. Terminal 120x may be used for a no-handoff user or a soft-handoff user. For simplicity, fig. 3 shows only the transmitter portion of terminal 120 x.

Within terminal 120x, an encoder/modulator 314 receives traffic data from a data source 312, as well as control data and other data from a controller 330. Traffic data is designated for transmission on a traffic channel x that has been assigned to terminal 120x by the serving sector for that terminal 120 x. Encoder/modulator 314 formats, codes, interleaves, and modulates the received data and provides modulation symbols (or simply "data symbols"). Each modulation symbol is a complex value for a particular point in a signal constellation (signal constellation) corresponding to the modulation mode used for that modulation symbol.

A transmit frequency hopping (TX FH) switch 316 receives the data symbols and provides them on the appropriate subbands for traffic channel x. Traffic channel x is associated with FH sequence x, which indicates the particular subband used for traffic channel x in each hop period T. Controller 330 may be based on the FH function f of the serving sector_s(k, T), generating FH sequence x. TX FH switch 316 may also provide pilot symbols on the pilot subbands and further provide null signal values for subbands not used for pilot or data transmission. For each OFDM symbol period, TXFH switch 316 provides N "transmit" symbols (including data symbols, pilot symbols, and zero signal values) for the N subbands.

An OFDM modulator 318 receives the N transmission symbols for each OFDM symbol period and providesCorresponding OFDM symbols. OFDM modulator 318 typically includes an Inverse Fast Fourier Transform (IFFT) unit and a cyclic prefix generator. For each OFDM symbol period, the IFFT unit transforms the N transmit symbols to the time domain using an inverse N-point fourier transform to obtain a "transformed" symbol comprising N time-domain "chips". Each chip is a complex value transmitted in one chip period. The cyclic prefix generator then repeats a portion of each transformed symbol to form a symbol containing N + C_pOne-chip OFDM symbol, where C_pIs the number of chips that are repeated. The repeated portion is commonly referred to as a cyclic prefix and is used to combat inter-symbol interference (ISI) caused by frequency selective fading. The OFDM symbol period corresponds to the duration of one OFDM symbol and is N + C_pOne chip period. An OFDM modulator 318 provides a stream of OFDM symbols.

A transmitter unit (TMTR)320 receives and processes the OFDM symbol stream to obtain a modulated signal. Transmitter unit 320 may further adjust the amplitude of the OFDM symbols and/or the modulation signal based on the power control signal received from controller 330. The modulated signal is transmitted from antenna 322 to the base stations in the active set for terminal 120 x.

Figure 4A is a block diagram of one embodiment of a base station 110x in a synchronous OFDMA system. Base station 110x is sector s_xThe fixed station of (1). For simplicity, fig. 4 shows only the receiver portion of base station 110 x.

Antenna 412 receives modulated signals transmitted by terminals within the coverage of base station 110 x. The received signal from antenna 412 may include: (1) from sector s_xOne or more modulated signals of a non-handover user; and (2) from sector s_xSoft handoff of one or more modulated signals of the user. The received signal is provided to a receiver unit (RCVR)414 and processed by the receiver unit (RCVR)414 to obtain samples. An OFDM demodulator 416 then processes the samples and provides "received" symbols, which are noise estimates for the combined transmitted symbols received by base station 110x and sent by all terminals. The OFDM demodulator 416 typically includes a cyclic prefix removal unit and an FFT unit. For theFor each OFDM symbol period, a cyclic prefix removal unit removes the cyclic prefix in each received OFDM symbol to obtain a received transformed symbol. Then, the FFT unit transforms each received transformed symbol to the frequency domain with an N-point FFT to obtain N received symbols for the N subbands.

An RX data processor 420 obtains the N received symbols for each OFDM symbol period and processes the symbols to obtain decoded data for transmission by each terminal to base station 110 x. The processing by RX data processor 420 is described in detail below. The decoded data for each terminal is provided to the data receiving means 422 for storage.

Controllers 330 and 430 control operation at terminal 120x and base station 110x, respectively. Memory units 332 and 432 provide storage for program codes and data used by controllers 330 and 430, respectively.

Figure 4B illustrates a block diagram of one embodiment of a base station 110y in an asynchronous OFDMA system. For an asynchronous system, the time of the secondary user and the time of the primary user may be different. OFDM demodulator/RX data processor 440 performs OFDM demodulation for each user based on the user's time. OFDM demodulator/RX data processor 440 also performs interference cancellation on the time-domain symbols, as described below.

In the embodiments described below, the sector s_xIs a primary user of a sector s_xAllocating users of a traffic channel, and sectors s_xIs divided by sector s_xOther sectors than the sector assign users of the traffic channel. Sector s_xThe primary user of may be sector s_xOr sectors s_xThe middle serving sector being sector s_xTo the soft handover user. Sector s_xIs sector s_xThe middle serving sector being a sectored sector s_xOther sectors than the soft handoff user.

Fig. 5 shows a block diagram of one embodiment of an RX data processor within base station 110x, as shown in fig. 4A, in a synchronous OFDMA system. In this embodiment, RX data processor 420 includes P data processors 510a through 510P for P primary users, an interference estimator 520, an interference canceller 530, and S data processors 540a through 540S for S secondary users, where P ≧ 1 and S ≧ 1.

For each OFDM symbol period, OFDM demodulator 416 provides N received symbols for the N subbands to data processors 510a through 510p and interference canceller 530. A data processor 510 is allocated to recover the data transmission from each primary user. The following describes the processing of the data transmission from the primary user 1 by the data processor 510 a. A traffic channel p1 is assigned to primary user 1, and a traffic channel p1 is associated with FH sequence p 1.

In data processor 510a, RX FH switch 514a receives the N received symbols for the N subbands in each OFDM symbol period. RX FH switch 514a provides the received data symbols for traffic channel p1 to demodulator/decoder 516a and provides the received pilot symbols for primary user 1 to channel estimator 518 a. Since the traffic channel p1 hops dynamically between subbands, RX FH switch 514a operates in concert with TX FH switch 316 at the terminal of primary user p1 to extract the received data symbols from the appropriate subbands of the traffic channel. The FH sequence provided to RX FH switch 514a is the same FH sequence provided to TX FH switch 316 at the primary user 1 terminal. Furthermore, these FH sequences are synchronized.

Channel estimator 518a obtains the received pilot symbols for primary user 1 from RX FH switch 514a (shown in fig. 5) or from the received symbols. Channel estimator 518a then obtains a channel estimate for primary user 1 based on the received pilot symbols. The channel estimate may include the following estimates: (1) channel gain between a terminal of primary user 1 and base station 110x for each sub-band used for data transmission; (2) signal strength of a pilot received from the primary user 1; and (3) other measurements.

Demodulator/decoder 516a may coherently demodulate the received data symbols from RX FH switch 514a with the channel estimate from channel estimator 518a to obtain a data symbol estimate for primary user 1. Demodulator/decoder 516a further demodulates (i.e., removes the symbol mapping), deinterleaves, and decodes the data symbol estimates to obtain the decoded traffic data for primary user 1. In general, the processing performed by the unit within the base station 110x of primary user 1 is complementary to the processing performed by the corresponding unit within the terminal of the primary user.

The data processors 510a to 510P provide decoded traffic data and channel estimates for the primary users 1 to P, respectively. The interference estimator 520 receives the decoded traffic data and channel estimates for the primary users 1 through P, estimates the interference caused by each of the P primary users, and provides the interference estimates for the P primary users to the interference canceller 530. Interference canceller 530 receives N received symbols for N subbands and interference estimates for the P primary users in each OFDM symbol period. For each OFDM symbol period, interference canceller 530 determines the total interference caused by the P primary users on the N subbands, subtracts the total interference from the received symbols for each subband, and provides N interference canceled symbols for the N subbands. The interference estimator 520 and the interference canceller 530 are described below.

A data processor 540 is allocated to resume data transmission from each secondary user. Each data processor 540 includes: RX FH switch 544, demodulator/decoder 546, and channel estimator 548, which operate in a manner similar to RX FH switch 514, demodulator/decoder 516, and channel estimator 518, respectively, within data processor 510. However, RX FH switch 544 in each data processor 540 is provided with N interference canceled symbols instead of the N received symbols for the N subbands. In addition, RX FH switch 544 within each data processor 540 operates in coordination with the TX FH switch at the secondary user terminal recovered by that data processor. Data processors 540a through 540S provide decrypted traffic data (and channel estimates) for sub-users 1 through S, respectively.

Fig. 6 is a block diagram of one embodiment of an interference estimator 520 and an interference canceller 530 within RX data processor 420 as shown in fig. 4A in a synchronous OFDMA system. In this embodiment, the interference estimator 520 includes P per-terminal interference estimators 620a through 620P for P primary users. A per-terminal interference estimator 620 is assigned to estimate the interference caused by each primary user. The following describes processing performed by the per-terminal interference estimator 620a to estimate interference caused by the primary user 1.

In the per-terminal interference estimator 620a, an encoder/modulator 622a receives the decoded traffic data of the primary user 1. Encoder/modulator 622a then encodes, interleaves, and modulates the decoded traffic data and provides data symbols. TX FH switch 624a receives the data symbols from encoder/modulator 622a and provides these symbols on the appropriate subband assigned to primary user 1's traffic channel p1, represented by the FH sequence p1 associated with the traffic channel. TX FH switch 624a may also provide pilot symbols on the appropriate subbands. TX FH switch 624a provides N transmit symbols for the N subbands in each OFDM symbol period. In general, the processing performed by the encoder/modulator 622a and the TX FH switch 624a is the same as the processing performed by the encoder/modulator 314 and the TX FH switch 316 at the terminal of the primary user 1.

Channel simulator 628a simulates the effect of the communication link between the terminal of primary user 1 and base station 110 x. Channel simulator 628a receives the transmit symbols from TX FH switch 624a and the channel estimate for primary user 1. Channel simulator 628a then processes the transmit symbols with a channel estimate to obtain an estimate of the interference caused by primary user 1. For example, channel simulator 628a may multiply the transmitted symbol on each subband by the channel gain estimate for that subband to obtain the interference component caused by primary user 1 on that subband.

The received symbols comprise sectors s_xSignal components of symbols transmitted by primary and secondary users. The interference estimate from channel simulator 628a is the signal component of the symbol transmitted by primary user 1. The interference estimate comprises N interference components for N subbands, where an interference component for a particular subband is zero if primary user 1 does not transmit data or pilot symbols on that subband.

The per-terminal interference estimators 620a to 620P process the decoded traffic data of the primary users 1 to P, respectively. Channel simulators 628 a-628P within each terminal interference estimator 620 a-620P provide interference estimates for primary users 1-P, respectively.

The interference canceller 530 includes N P-input adders 630a through 630N and N two-input adders 632a through 632N, i.e., a set of adders 630 and 632 for each of the N subbands. Interference canceller 530 receives the N received symbols for the N subbands from OFDM demodulator 416 and receives interference estimates for primary users 1 through P from interference estimators 620a through 620P. Within interference canceller 530, an adder 630a receives and adds the interference components caused by the P primary users on subband 1 and then provides the total interference on subband 1. Each of the other N-1 adders 630 of sub-bands 2 through N receives and adds the interference components caused by the P primary users on the associated sub-band and then provides the total interference on that sub-band. Adder 632a receives the total interference on subband 1 and subtracts it from the received symbol for subband 1 and provides an interference canceled symbol for subband 1. Each of the other N-1 adders 632 for subbands 2 through N similarly receives the total interference on the associated subband and subtracts it from the received symbols for that subband and then provides interference canceled symbols for that subband. Adders 632a through 632N provide N interference canceled symbols for the N subbands for each OFDM symbol period.

Figure 7 is a block diagram illustrating one embodiment of an OFDM demodulator/RX data processor 440 within base station 110y as shown in figure 4B in an asynchronous OFDMA system. In this embodiment, OFDM demodulator/RX data processor 440 includes P primary user data processors 710a through 710P, an interference estimator 720, an interference canceller 730, and S secondary user data processors 740a through 740S, where P ≧ 1 and S ≧ 1.

The recovered symbols from receiver unit 414 are provided to each of data processors 710a through 710 p. Each data processor 710 includes: OFDM demodulator 712, RX FH switch 714, demodulator/decoder 716, and channel estimator 718. An OFDM demodulator 712 within each data processor 710 performs OFDM demodulation on the received symbols based on the time allocated to the primary user for that data processor and provides symbol estimates for the N subbands. RX FH switch 714, demodulator/decoder 716, and channel estimator 718 then operate on the symbol estimates in a manner similar to RX FH switch 514, demodulator/decoder 516, and channel estimator 518 described in fig. 5. Each data processor 740 also includes an OFDM demodulator 742 that performs OFDM demodulation on the interference-canceled symbols based on the time allocated to the secondary user of that data processor.

Fig. 8 shows a block diagram of one embodiment of an interference estimator 720 and an interference canceller 730 within the OFDM demodulator/RX data processor 440 shown in fig. 4B in an asynchronous OFDMA system. In this embodiment, interference estimator 720 includes P per-terminal interference estimators 820a through 820P for P primary users. A per-terminal interference estimator 820 is assigned to estimate the interference caused by each primary user. Each per-terminal interference estimator 820 includes: encoder/modulator 822, TX FH switch 824, OFDM modulator 826, and channel simulator 828. Encoder/modulator 822 and TX FH switch 824 operate in the same manner as encoder/modulator 622 and TX FH switch 624 in fig. 6. TX FH switch 824 provides N transmit symbols for the N subbands in each OFDM symbol period. An OFDM modulator 826 then performs OFDM modulation on the N transmit symbols for each OFDM symbol period and provides time domain symbols.

Channel simulator 828 then processes the time domain symbols with the channel estimates for the assigned primary user to obtain an estimate of the interference caused by that primary user. Since different primary users are associated with different times of the asynchronous system, channel simulator 828 also performs sample rate conversion to time align the interference estimates from the channel simulator with the received symbols.

Interference canceller 730 includes a P-input summer 830 and a two-input summer 832. Interference canceller 730 receives the received symbols from receiver unit 414 and interference estimates for primary users 1 through P from per-terminal interference estimators 820a through 820P, respectively. Within interference canceller 730, adder 830 cancels the interference caused by the P primary users and provides the total interference. Adder 832 subtracts the total interference from the received symbols and provides interference canceled symbols, which are processed by data processors 740a through 740S for the S secondary users.

The embodiment shown in fig. 5 and 6 suggests: the interference caused by all P primary users is estimated and cancelled, and the data transmission from S secondary users is recovered. Sector s_xThe primary user of (a) may be a soft handoff user that is power controlled by multiple sectors in the user's active set. Sector s if data transmission from the primary user is power controlled to enable recovery by other sectors in the active set_xThe base station 110x of (a) cannot decode the data transmission from the primary user. If the data transmission from any primary user cannot be decoded, then base station 110x will not attempt to estimate and cancel the interference caused by that primary user. The base station may use the partially decoded data to cancel some of the interference.

The above description of fig. 5 and 6 also applies to such an embodiment: sector s_xOne primary user of is sector s_xOf non-handed-over users, sectors s_xIs a sector s_xRegardless of the serving sector of the soft-handoff user.

For the embodiments shown in fig. 5 and 6, after estimating and canceling the interference caused by the primary user, the primary user is decoded first, and then the secondary user is decoded. Of course, the secondary user may be decoded first and then the primary user may be decoded after estimating and canceling the interference caused by the secondary user. In general, base station 110x may decode data transmissions from users in any order. The interference caused by each successfully decoded user can be estimated and cancelled, thereby improving the signal quality of the remaining undecoded users. However, system implementation can be simplified if the power control of the non-handoff users enables them to be successfully decoded in the presence of interference from soft handoff users. In this case, the non-handed-off user is decoded first, and then the soft-handed-off user is decoded.

For simplicity, FIGS. 5 and 6 show a parallel design in which: (1) a data processor 510 and a per-terminal interference estimator 620 are provided for each primary user; and (2) one data processor 540 is provided for each secondary user. A time division multiplexing design (TDM) may also be used in which a data processor 510 is provided for time sharing by all primary and secondary users, and a per-terminal interference estimator 620 is provided for time sharing by all primary users.

Fig. 9 is a flow diagram of a process 900 for transmitting data in a wireless communication system, such as a frequency hopping OFDMA system. Process 900 may be performed for terminals in soft handoff with multiple base stations using multiple sectors.

First, an assignment of a traffic channel is obtained from a first base station (step 912). For a frequency hopping OFDMA system, the assigned traffic channel is associated with a FH sequence that represents a specific subband to use for data transmission in each time interval (i.e., each hop period). The data is encoded and modulated to obtain data symbols (step 914). For a frequency hopping OFDMA system, the data symbols are provided on the subbands indicated by the FH sequence (step 916). The data symbols are further processed (e.g., OFDM modulated) for transmission to the first and second base stations over the assigned traffic channels (step 918).

The traffic channels assigned by the first base station are orthogonal to each other and are not orthogonal to the traffic channels assigned by the second base station. For a frequency hopping OFDMA system, the traffic channels assigned by the first base station and the second base station are each associated with a respective FH sequence. The FH sequences for traffic channels assigned by the first base station are orthogonal to each other and are not orthogonal to the FH sequences for traffic channels assigned by the second base station.

Fig. 10 is a flow diagram of a process 1000 for receiving data transmissions from multiple terminals in a wireless communication system, such as a frequency hopping OFDMA system. Process 1000 may be performed by a base station for each sector. For clarity, the following describes the sector s_xIs performed by base station x.

First, received symbols are obtained (step 1012). The receiving of the symbols comprises: (1) at least one data transmission on at least one "primary" traffic channel from at least one primary terminal; and (2) at least one data transmission on at least one "secondary" traffic channel from at least one secondary terminal. The primary traffic channel is a traffic channel assigned by base station x, and the secondary traffic channel is a channel assigned by another base station (e.g., a neighboring base station of base station x). The primary traffic channels are orthogonal to each other and are not orthogonal to the secondary traffic channels. The primary traffic channel may be pseudo-random with respect to the secondary traffic channel. The primary terminal is a terminal to which a primary traffic channel is assigned by base station x, and the secondary terminal is a terminal to which a secondary traffic channel is assigned by the other base station. Each secondary terminal is in soft handoff with at least two base stations, including base station x, and may be assigned a secondary traffic channel by a base station other than base station x.

For an OFDMA system, the received symbols for the N subbands are obtained from an OFDM demodulator. For an OFDMA system, each traffic channel is also associated with a corresponding FH sequence. The "primary" FH sequences for the primary traffic channels are orthogonal to each other and are not orthogonal to the "secondary" FH sequences for the secondary traffic channels.

The received symbols are processed to obtain decoded data for each master terminal (step 1014). The interference caused by the primary terminal is estimated (step 1016) and canceled from the received symbols to obtain interference-canceled symbols (step 1018). The interference-canceled symbols are then processed to obtain decoded data for each secondary terminal (step 1020).

The processing for each master terminal includes: (1) acquiring a received symbol on a sub-band indicated by a main FH sequence of a main traffic channel allocated to the main terminal; (2) obtaining a channel estimate for the primary terminal (e.g., based on pilot symbols received from the primary terminal); and (3) demodulating and decoding (e.g., using the channel estimate of the primary terminal) the received symbols of the primary terminal to obtain decoded data for the primary terminal. In a similar manner, processing for each secondary terminal is performed, but for the interference canceled symbols, rather than the received symbols.

The interference caused by each master terminal may be estimated as follows: (1) encoding and modulating the decoded data of the main terminal; (2) providing the data symbol on a subband indicated by an FH sequence assigned to the primary terminal; and (3) processing the data symbols with a channel estimate to obtain interference caused by the primary terminal. The interference caused by each master terminal may be combined to obtain the total interference caused by the master terminals.

The techniques described herein may be used for frequency hopping OFDMA systems and other types of wireless communication systems. For example, these techniques may be used in systems employing other multicarrier modulation techniques, such as Discrete Multitone (DMT). These techniques may also be used for wireless communication systems that do not use multi-carrier modulation and wireless communication systems that do not employ frequency hopping.

The techniques described herein may be used in systems where traffic channels are otherwise defined. For frequency hopping OFDMA systems, the traffic channel is defined by an associated FH sequence that represents a specific subband to use in each hop period. For Time Division Multiplexed (TDM) systems, data may be transmitted in time slots, and different time slots may be allocated for multiple traffic channels. The traffic channels for each sector may be defined to be orthogonal to each other such that no two traffic channels use the same time slot. The traffic channels of different sectors may be pseudo-random so that the traffic channel of one sector and the traffic channel of another sector may use the same time slot (and thus they will collide). The techniques described herein may also be used for this TDM system. Each soft handoff user is assigned a traffic channel by its serving sector. Each sector recovers data transmissions from primary users of the sector, cancels interference caused by the primary users, and then recovers data transmissions from secondary users of the sector.

As described above, the techniques described herein may be used to support soft handoff on the reverse link. These techniques may also be used to support softer handoffs in which a terminal communicates using multiple sectors of the same cell. The same processing may be performed at the base station and the terminal for soft and softer handover.

The techniques described herein may also be used for the forward link. For example, a terminal may receive a particular user data transmission from one base station and an overhead transmission (e.g., a broadcast transmission) from multiple base stations on the forward link. The terminal may process its received signal to recover user-specific data transmissions from the base station, estimate and cancel interference caused by the user-specific data transmissions, and process the interference-canceled signal to recover overhead transmissions from multiple base stations.

The techniques described herein may be implemented in various ways. For example, these techniques may be implemented in hardware, software, or a combination of hardware and software. For a hardware implementation, the processing units within a base station (e.g., data processors 510 and 540, interference canceller 520, interference canceller 530, etc.) may be implemented as one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, and combinations thereof. The processing units within the terminal (e.g., encoder/modulator 314, TX FH switch 316, OFDM modulator 318, etc.) may also be implemented in one or more ASICs, DSPs, and the like.

For a software implementation, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. These software codes may be stored in memory units (e.g., memory unit 332 in fig. 3 and memory unit 432 in fig. 4) and executed by processors (e.g., controllers 330 and 430). The memory unit may be implemented within the processor or external to the processor, and if implemented external to the processor, the memory unit may be communicatively coupled to the processor via various means as is known in the art.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (35)

1. A method for receiving a data transmission in a wireless communication system, comprising:

obtaining at least one received symbol for data transmission on at least one primary traffic channel from at least one primary terminal and at least one received symbol for data transmission on at least one secondary traffic channel from at least one secondary terminal, wherein the at least one primary traffic channel is orthogonal to each other and is not orthogonal to the at least one secondary traffic channel;

processing the received symbols to obtain decoded data for each of the at least one master terminal;

estimating interference caused by the at least one master terminal;

canceling the interference caused by the at least one primary terminal from the received symbols to obtain interference-canceled symbols; and

processing the interference-canceled symbols to obtain decoded data for each of the at least one secondary terminal.

2. The method of claim 1, wherein the wireless communication system is a frequency hopping communication system.

3. The method of claim 2, wherein the at least one primary traffic channel and the at least one secondary traffic channel are each associated with a respective Frequency Hopping (FH) sequence that represents a particular one of a plurality of subbands to use for data transmission in each time interval.

4. The method of claim 1, wherein the wireless communication system is a synchronous system.

5. The method of claim 1, wherein the wireless communication system is an asynchronous system.

6. A method for receiving a data transmission at a base station in a wireless Frequency Hopping (FH) communication system, comprising:

obtaining received symbols of a plurality of sub-bands;

processing the received symbols to obtain decoded data for each of at least one primary terminal, wherein at least one primary FH sequence for data transmission is assigned to the at least one primary terminal, and wherein the at least one primary FH sequence is orthogonal to each other;

estimating interference caused by the at least one master terminal;

canceling the interference caused by the at least one primary terminal from the received symbols to obtain interference-canceled symbols; and

processing the interference canceled symbols to obtain decoded data for each of at least one secondary terminal, wherein at least one secondary FH sequence for data transmission is assigned to the at least one secondary terminal, and wherein the at least one secondary FH sequence is non-orthogonal to the at least one primary FH sequence.

7. The method of claim 6, wherein the base station allocates the at least one primary FH sequence to the at least one primary terminal, and wherein a neighboring base station of the base station allocates the at least one secondary FH sequence to the at least one secondary terminal.

8. The method of claim 6, wherein each of the at least one secondary terminal is in soft handoff with at least two base stations including the base station.

9. The method of claim 8, wherein a first secondary terminal of the at least one secondary terminal is in soft handoff with at least two base stations of at least two different sectors of a cell in the system.

10. The method of claim 8, wherein a first secondary terminal of the at least one secondary terminal is in soft handover with at least two base stations of two different cells in the system.

11. The method of claim 8, wherein one of the at least two base stations that is not the base station assigns one secondary FH sequence for each of the at least one secondary terminal.

12. The method of claim 6, wherein the at least one master terminal comprises a terminal that is not in soft handoff and communicates only with the base station.

13. The method of claim 12, wherein the at least one master terminal further comprises a terminal in soft handoff and assigned an FH sequence by the base station.

14. The method of claim 6, wherein the at least one primary FH sequence is pseudo-random with respect to the at least one secondary FH sequence.

15. The method of claim 6, wherein the processing the received symbols comprises:

for each of the at least one master terminal,

obtaining received symbols on a subband indicated by a primary FH sequence assigned to the primary terminal;

acquiring channel estimation of the main terminal; and

demodulating and decoding the received symbols of the master terminal to obtain decoded data of the master terminal.

16. The method of claim 6, wherein the estimating step comprises:

for each of the at least one master terminal,

encoding and modulating the decoded data of the main terminal to obtain data symbols of the main terminal;

providing the data symbols for the primary terminal on a subband indicated by a primary FH sequence assigned to the primary terminal; and

processing the data symbols of the primary terminal using a channel estimate of the primary terminal to obtain interference caused by the primary terminal; and

combining the interference caused by each of the at least one master terminal to obtain the interference caused by the at least one master terminal.

17. The method of claim 6, wherein the processing the interference canceled symbols comprises:

for each of the at least one secondary terminal,

obtaining interference canceled symbols on subbands indicated by secondary FH sequences assigned to the secondary terminal; and

demodulating and decoding the interference-canceled symbols of the secondary terminal to obtain the decoded data of the secondary terminal.

18. The method of claim 6, wherein the wireless communication system is an Orthogonal Frequency Division Multiple Access (OFDMA) communication system.

19. An apparatus in a wireless Frequency Hopping (FH) communication system, comprising:

an obtaining module, configured to obtain received symbols of multiple subbands;

a processing module for processing the received symbols to obtain decoded data for each of at least one primary terminal, wherein at least one primary FH sequence for data transmission is assigned to the at least one primary terminal, and wherein the at least one primary FH sequence is orthogonal to each other;

an estimation module for estimating interference caused by the at least one master terminal;

a cancellation module configured to cancel the interference caused by the at least one primary terminal from the received symbols to obtain interference-cancelled symbols; and

a processing module for processing the interference canceled symbols to obtain decoded data for each of at least one secondary terminal, wherein at least one secondary FH sequence for data transmission is assigned to the at least one secondary terminal, and wherein the at least one secondary FH sequence is non-orthogonal to the at least one primary FH sequence.

20. An apparatus in a wireless Frequency Hopping (FH) communication system, comprising:

at least one first data processor configured to process received symbols to obtain decoded data for each of at least one primary terminal, wherein at least one primary FH sequence for data transmission is assigned to the at least one primary terminal, and wherein the at least one primary FH sequences are orthogonal to each other;

an interference estimator for estimating interference caused by the at least one master terminal;

an interference canceller configured to cancel the interference caused by the at least one master terminal from the received symbols to obtain interference-cancelled symbols; and

at least one second data processor configured to process the interference canceled symbols to obtain decoded data for each of at least one secondary terminal, wherein at least one secondary FH sequence for data transmission is assigned to the at least one secondary terminal, and wherein the at least one secondary FH sequence is non-orthogonal to the at least one primary FH sequence.

21. The apparatus of claim 20, wherein each of the at least one first data processor is assigned to a respective one of the at least one master terminal, and wherein the first data processor of each master terminal comprises:

a switch to obtain received symbols on a subband indicated by a primary FH sequence assigned to the primary terminal;

a channel estimator for acquiring a channel estimate of the master terminal; and

a demodulator and a decoder for demodulating and decoding the received symbols of the main terminal to obtain the decoded data of the main terminal.

22. The apparatus of claim 20, wherein the interference estimator comprises at least one per-terminal interference estimator each for estimating interference caused by a respective one of the at least one master terminal, and wherein the per-terminal interference estimator for each master terminal comprises:

an encoder and a modulator, configured to encode and modulate the decoded data of the main terminal to obtain a data symbol of the main terminal;

a switch to provide the data symbols for the primary terminal on a subband indicated by a primary FH sequence assigned to the primary terminal; and

a channel simulator for processing the data symbols of the main terminal by using the channel estimation of the main terminal to obtain the interference caused by the main terminal.

23. A processor-readable medium for storing instructions for:

obtaining received symbols of a plurality of sub-bands;

processing the received symbols to obtain decoded data for each of at least one primary terminal, wherein at least one primary Frequency Hopping (FH) sequence for data transmission is assigned to the at least one primary terminal, and wherein the at least one primary FH sequence is orthogonal to each other;

estimating interference caused by the at least one master terminal;

canceling the interference caused by the at least one primary terminal from the received symbols to obtain interference-canceled symbols; and

processing the interference canceled symbols to obtain decoded data for each of at least one secondary terminal, wherein at least one secondary FH sequence for data transmission is assigned to the at least one secondary terminal, and wherein the at least one secondary FH sequence is non-orthogonal to the at least one primary FH sequence.

24. A method of transmitting data from a terminal in a wireless communication system, comprising:

obtaining the allocation of a traffic channel from a first base station;

encoding and modulating data to obtain data symbols; and

processing the data symbols transmitted to the first and second base stations over the traffic channel, wherein the traffic channels allocated by the first base station are orthogonal to each other and are non-orthogonal to the traffic channels allocated by the second base station.

25. The method of claim 24, wherein the first base station receives, processes, and cancels transmissions from other terminals to which other traffic channels that are not orthogonal to the traffic channels assigned to the terminals are assigned, before resuming the transmissions from the other terminals.

26. The method of claim 24, wherein the second base station receives, processes, and cancels transmissions from other terminals assigned other traffic channels by the second base station before resuming transmissions from the terminals.

27. The method of claim 24, wherein the wireless communication system is a frequency hopping communication system.

28. The method of claim 27, wherein the traffic channel assigned by the first base station and the traffic channel assigned by the second base station are each associated with a respective Frequency Hopping (FH) sequence that indicates a particular one of a plurality of subbands to use for data transmission in each time interval.

29. The method of claim 24, wherein the first and second base stations are for two different sectors of a cell in the system.

30. The method of claim 24, wherein the first and second base stations are for two different cells in the system.

31. A method for transmitting data in a wireless Frequency Hopping (FH) communication system, comprising:

obtaining allocation of FH sequences from a first base station;

encoding and modulating data to obtain data symbols;

providing the data symbols on subbands indicated by the FH sequence; and

processing the data symbols to be transmitted to the first base station and a second base station, wherein the FH sequences assigned by the first base station are orthogonal to each other and are non-orthogonal to the FH sequences assigned by the second base station.

32. The method of claim 31, wherein the FH sequences assigned by the first base station are pseudo-random with respect to the FH sequences assigned by the second base station.

33. An apparatus in a wireless Frequency Hopping (FH) communication system, comprising:

an acquisition module for acquiring allocation of FH sequences from a first base station;

the encoding and modulation module is used for encoding and modulating data to obtain a data symbol;

means for providing the data symbols on subbands indicated by the FH sequence; and

a processing module configured to process the data symbols to be transmitted to the first base station and the second base station, wherein the FH sequences assigned by the first base station are orthogonal to each other and are not orthogonal to the FH sequences assigned by the second base station.

34. An apparatus in a wireless Frequency Hopping (FH) communication system, comprising:

a controller for obtaining an allocation of FH sequences from a first base station;

an encoder and a modulator for encoding and modulating data to obtain data symbols;

a switch to provide the data symbols on subbands indicated by the FH sequence; and

an Orthogonal Frequency Division Multiplexing (OFDM) modulator for processing the data symbols to be transmitted to the first and second base stations, wherein the FH sequences assigned by the first base station are orthogonal to each other and are non-orthogonal to the FH sequences assigned by the second base station.

35. A processor-readable medium for storing instructions for:

obtaining allocation of FH sequences from a first base station;

encoding and modulating data to obtain data symbols;

providing the data symbols on subbands indicated by the FH sequence; and

processing the data symbols to be transmitted to the first base station and a second base station, wherein the FH sequences assigned by the first base station are orthogonal to each other and are non-orthogonal to the FH sequences assigned by the second base station.