Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/02—Arrangements for detecting or preventing errors in the information received by diversity reception
  • H04L1/06—Arrangements for detecting or preventing errors in the information received by diversity reception using space diversity
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
  • H04B7/0802—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using antenna selection
  • H04B7/0805—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using antenna selection with single receiver and antenna switching
  • H04B7/0814—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using antenna selection with single receiver and antenna switching based on current reception conditions, e.g. switching to different antenna when signal level is below threshold

Definitions

• This invention relates to the field of portable communication transceivers and specifically to a portable transceiver circuit which determines the quality of a received signal and directs the tranceiver to select an alternative antenna if the signal quality deteriorates below a predetermined level.
• Portable radio transceivers are used in several facets of communications technology.
• Portable trans ⁇ ceivers can be found in paging systems, two-way communication systems such as those used by police and other public servants, and more recently portable receivers have found use in portable data terminals which are used to communicate with a host computer over a radio link.
• Portable data terminals provide computer diagnostics and expanded computer power in the portable terminal.
• Typical portable paging receivers in the past have incorporated loop-type antennas which are typically
• Portable units which contain both a receiver and transmitter are utilized in public service and private industry where communication between a number of units is desirable.
• the units typically contain a receiver and transmitter used in combination with an external helical, monopole or dipole antenna. These antennas are respon ⁇ sive to the electrical field of an RF signal and provide superior reception and transmission characteristics, when the antenna is located externally to the portable device housing. In addition, helical and monopole antenna performance is degraded substantially when the antenna is operated in close proximity to a human body.
• a paging receiver is. normally worn on the body when in use. Unlike the pager, a portable transceiver is utilized in many different environments. It may be handheld in front of the face, worn on the hip, or placed on a conducting or non-conducting surface.
• portable communication devices which are capable of transmitting and receiving data in cooperation with a host computer. These devices are for instance useful to servicemen who use the portable terminal to perform on-site computer testing and diagnostics, and to keep records thereof. It is desirable to manufacture a portable data terminal as small as possible, so the terminal can be transported easily. In addition, it is also desirable to provide a portable data terminal with an antenna system which is completely enclosed within the terminal housing. This feature enhances the portability of 'the data terminal, as well as providing protection for the terminal antenna system.
• terminals may be carried in the hand, worn on the hip, put in a coat pocket, used on a desk, or put into a service tool kit.
• the orientation of the unit, as well as its physical environment is constantly changing as it is utilized from one time to the next.
• the portable data terminal Since the portable data terminal is operated in a number of distinct environments and orientations, it is necessary to provide an antenna system which is adaptable to a changing environment. Adaptability is especially useful when the portable data terminal is used in close proximity to a human body.
• the receiver In an adaptable antenna system, the receiver must include a means for alternatly activating antennas in response to the quality of a received signal.
• Prior art antenna switching devices have typically based the antenna switching decision on the signal strength of an incoming RF signal. This technique switches antennas when the incoming signal drops below a predetermined threshold. To implement a signal strength based antenna decision, expensive RF circuitry is required to process signal strength information. In addition, signal strength based antenna switching is prone to "chattering" when the signal level for each antenna is below a predetermined threshold.
• the invention contemplates an antenna switching circuit and technique which is used to control an adaptable antenna system in a portable trans ⁇ DCver.
• the inventive antenna switching circuit is coupled to the audio output of a receiver, which is configured to provide a data output signal.
• the receiver is coupled to a bit quality detector which samples each incoming data bit at four times the data rate. Each data cycle is stored in a shift register. The data sample corresponding to the middle of the data bit is retained as the value of the data bit and the four data bit samples are compared to generate a bit noise flag bit. If the bit transition jitter is less than + 1/4 bit, the noise flag is 0 otherwise the bit noise flag is set to 1.
• the incoming data stream and bit noise flag stream is then coupled to a microcomputer which operates in conjunction with the bit quality and data storage registers. When 8 data bits and the corresponding 8 noise flag bits have been accumulated, the bits are read into the microcomputer memory and processed in accordance
• the microprocessor retains 14 bytes of previous bit noise flag information.
• the microcomputer then - compares the flag rate being generated by the presently connected antenna with the flag rate which was generated by the' previously connected antenna. If the antenna presently connected produces a flag rate higher than the previously connected antenna, the microprocessor will pause and switch antennas at a time which minimizes bit errors due to switching transients.
• Figure 1 is a perspective drawing of a portable data receiver such as one which would incorporate the preferred embodiment of the present invention.
• FIG. 2 is a block diagram of an antenna system which would incorporate an embodiment of the present invention.
• Figure 3 is a illustration of the sampling scheme for determining bit quality in accordance with the present invention.
• Figure 4 is an electrical schematic of a circuit which generates bit quality information bits utilized by the present invention.
• FIG. 5 is a flow diagram which details the operation of the present invention.
• FIG. 1 shows a perspective drawing of a portable data communication device such as one which would incorporate the preferred embodiment of the present invention.
• the portable transceiver 10 incorporates a display 12 and a keyboard 11 and is used to communicate with a host computer.
• the portable transceiver 10 transmits and receives modulated data and can be used to provide on-site computer diagnostics.
• the portable transceiver 10 is constructed of a plastic housing which encases the terminal and radio electronic circuits, as well as an adaptable antenna system including a plurality of antennas which may be optimized for specific environmental conditions, for example, on the body versus off the body use.
• FIG. 2 shows an electrical schematic and block diagram of a data receiver which would utilize the pre ⁇ ferred embodiment of the present invention.
• the data terminal includes two antennas 14, 13 which are coupled to diodes 21, 26. The antennas are selectively activated through inductors 22, 27 by placing a control voltage on terminals "A" or "B". Antennas 14, 13 are then coupled to a receiver 28 through capacitors 23, 24. The receiver 28 processes the received signal and converts it to a lower frequency signal of the desired form, in this case binary data at approximately 4800 bits/sec.
• the receiver data output is then coupled to a bit quality detector 30 which generates a binary signal corresponding to the binary data signal which provides a flag indicating the quality of a received bit.
• the bit quality detector 30 evaluator circuit will be discussed in more detail later.
• the bit quality detector 30 is coupled to a micro ⁇ processor 31 which processes the incoming data and bit quality information in accordance with the present invention.
• the microprocessor 31 then selectively activates antenna 14 or 15 depending on the quality of the - 1 -
• FIG. 3 is an illustration of the sampling scheme for determining bit quality in accordance with the present invention. As shown in Figure 3, each incoming data bit is sampled four times. According to the present invention, a data bit of acceptable integrity is defined as having less than _+ 1/4 bit transition time jitter.
• Figure 4 shows an electrical schematic of a circuit in bit quality detector 30 in Figure 2 which generates noise flag bit information in accordance with the present invention.
• the bit noise flag generator circuit consists of a series of flip-flops 40, 42, 44 which are configured as a 3 bit shift register. Samples are shifted into the three bit shift register at four times the data rate as shown by terminal 4X coupled to flip-flops 40, 42 and 44. The three outputs of this shift register provide the four sample per bit information required to recover clock and data and generate bit noise flags.
• a separate circuit decodes the data stream and produces a clock signal at the clock rate, a clock signal at twice the data rate and a clock signal at four times the data rate.
• the clock recovery circuit could be any conventional digital phase locked loop configured to lock the detector clock onto the incoming data stream.
• the four samples occur on the rising edge of 4X serial data clock.
• the 1X and 2X clocks are derived from the 4X clock by simple divide by 2 stages.
• the 1X and 2X clocks are used to uniquely identify the position of the four samples as they are shifted through the 3 bit register.
• the recovered data signal is derived from the output of flip-flop 40 and corresponds to sample 3 of Figure 3. The data sample is then shifted to the 8 bit data register 56 on each falling edge of the 1X clock.
• the bit noise flag information is generated by logic gates 46, 48 and 50.' The bit noise flag bit is shifted into the 8 bit BNF register 54 on the rising edge of the BNF clock (BNFC) . This occurs when flip-flop 40 stores sample 4, flip-flop 42 stores sample 3, and flip-flop 44 stores sample 2.
• the exclusive OR gates 48, 46 and OR gate 50 are coupled so that they generate an output according to the logical relationship.
• FIG. 5 shows a flow diagram which defines the micro ⁇ processor (31 of Figure 2) operation in accordance with the present invention.
• the process of the present invention keeps a running total of how many bits are flagged and which antenna is connected when each byte's worth of data received.
• the inventive process decides that the antenna is to be switched if and only if there is at least one flag bit that is a 1 in the most recently received byte and the flag rate from the non-attached antenna (FR2) is less than the flag rate of the attached antenna (FR1).
• Flag rate 2 (FR2) is defined as the number of flags received in the last fourteen bytes when the non-attached antenna 2 was attached divided by the number of bytes when the non-attached antenna was attached.
• FR2 is equal to zero if non-attached antenna was not attached during the last 14 bytes.
• Flag rate 1 (FR1) for the attached antenna FR1 is defined in the same manner. When an antenna switch is effected, the number of flags in the byte where the antenna switch occurred is set
• the inventive process also causes the switching action to occur at a particular time before the next bit enters the antenna terminals.
• the microprocessor 31 in Figure 2 is adjusted to switch the antenna about 50 microseconds before the bit transition enters the antenna terminals. This feature allows the antenna system to switch antennas at a time which minimizes bit errors due to switching transients.
• the program shown in Figure 5 is initated every time the BNF and data registers (54, 56 in Figure 4) have accumulated eight bits.
• Item 70 instructs the microprocessor to read the contents of the data and BNF registers into the micro ⁇ processor RAM. For the purposes of the present invention, 14 bytes of previous BNF information for the antennas are also retained in RAM.
• decision 72 selects item 78 which counts and stores the BNF information of the latest byte.
• the program proceeds to decision 80 which compares the relative flag rates FRl and FR2 of the two antennas.
• the antenna switching system examines bit quality information generated by an electronic circuit and switches antennas based on the relative bit flag rate being produced by each antenna.
• the invention effects antenna switches at a time chosen to minimize bit error due to switching transients.

Landscapes

• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Radio Transmission System (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=24034884

Family Applications (1)

Country Status (4)

Families Citing this family (4)

Family Cites Families (5)

• 1984
  • 1984-06-27 AU AU31502/84A patent/AU3150284A/en not_active Abandoned
  • 1984-06-27 EP EP19840902741 patent/EP0148258A1/de not_active Withdrawn
  • 1984-06-27 WO PCT/US1984/000999 patent/WO1985000482A1/en not_active Ceased
  • 1984-06-29 CA CA000457944A patent/CA1220545A/en not_active Expired

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events