HK1018992A - Impairment determination for a diversity antenna selection process - Google Patents

Description

Impairment determination for diversity antenna selection process

Technical Field

The present invention is directed generally to wireless communications, and more particularly to antenna diversity techniques, and more particularly to diversity reception of digital signals for use in fixed wireless access applications.

Background

In wireless communications, multipath fading is a well-known cause of received signal level fluctuations and, therefore, communication degradation.

Diversity reception has been widely performed as a method of reducing such fading. For example, if the two antennas are separated from each other by a predetermined distance, the probability that signals from the two antennas are simultaneously attenuated to the same degree is remarkably reduced, and thus higher reliability is achieved. For example, when two antennas are used instead of one antenna, the signal-to-interference margin can be increased by as much as 10 dB. Various diversity reception methods are known.

In most cases, a system requires a priori knowledge of the Received Signal Strength Indication (RSSI) of all antennas that are selectable if it is considered "perfect" diversity. For many prior art diversity systems, such information is only available using dual receivers. In such an arrangement, the RSSI of the signal received at each antenna is continuously monitored and the best antenna is selected. This implementation adds considerable expense to the radio receiver.

Some prior art solutions teach the use of two or more antennas and one receiver circuit. Antenna selection circuitry switches between antennas in response to received signal strength indications generated by the receiver. However, without a dual receiver, unused antennas must be periodically tried, resulting in instantaneous interruption of bits (missing or corrupted bits) or frames (missing or corrupted frames) in the received data whenever the "tested" antenna has a poor RSSI.

Furthermore, in the past these prior art diversity systems have been of particular concern with base stations and in part less relevant to user terminals, since the antennas were required to be physically separated by a minimum distance of one-half wavelength. This practical separation of antennas typically makes it impractical to combine such techniques in small, compact mobile terminals. Moreover, as noted, diversity techniques typically utilize dual receivers, which are acceptable to the base station but uneconomical to be effective for the terminal.

However, the multipath fading problem is more problematic for fixed wireless access terminals than for mobile terminals in many ways, since the user terminal is fixed and therefore cannot be moved by the user in response to poor reception as a result of deep fading.

Furthermore, even in cases where multipath fading does not present a significant problem, the quality of reception may still be poor due to co-channel interference (CCI) in the forward link. This problem is particularly acute in high capacity cellular networks where it is desirable to reuse frequencies many times to reduce the signal-to-interference ratio (SIR). However, conventional prior art diversity solutions designed to switch antennas based on a comparison of Received Signal Strength Indications (RSSI) between antennas generally do not address such a problem.

Another problem that the prior art known to the present inventors cannot properly solve is: some users have their radio link performance limited by forward link signal strength, while other users have their forward link quality limited by co-channel interference (CCI) due to high user density. Furthermore, there is typically insufficient prior knowledge to predict which of these two problems is the main cause of poor reception quality. Furthermore, the two impairments (i.e., fading and CCI) may occur at different times and are independent of each other. Accordingly, there is a need for improved diversity systems that can improve reception regardless of which impairment results in reduced reception.

Summary of The Invention

An aspect of the present invention provides a diversity selection procedure and a terminal for performing the same, while also providing for Mobile Assisted Handover (MAHO) measurements. The present inventors have realised that this is a particular advantage for fixed radio access (FWA) terminals which do not move in and out of the cell and therefore do not set up a handover beforehand. To this end FWA terminals with both diversity and MAHO are provided, which may improve service by switching antennas for relatively short term problems or allow switching to another base station (if available) for persistent problems.

Another aspect of the invention is directed to a process and apparatus for performing antenna diversity that first evaluates the nature of the impairment that caused poor reception and then switches antennas accordingly. Such a system is particularly suitable for fixed wireless access terminals using digital radio communication.

It should be noted that these techniques can be applied to any type of antenna scheme and that the signals can be suitably decorrelated, regardless of whether such decorrelation is achieved through spatial or polarization diversity.

Brief description of the drawings

The invention, together with further objects and advantages thereof, will be further understood from the following description of exemplary embodiments taken in conjunction with the accompanying drawings, in which:

fig. 1 is a schematic block diagram of a wireless access terminal incorporating a preferred embodiment of the present invention.

Fig. 2 is a flow diagram illustrating the steps of a diversity selection process performed by the baseband microcontroller of fig. 1 according to one embodiment of the invention.

Fig. 3 is a timing reference diagram illustrating another aspect of the process of fig. 2 in accordance with one embodiment of the present invention.

Fig. 4 is a series of flow diagrams illustrating the steps of a diversity selection process performed by a baseband microcontroller according to another embodiment of the present invention.

Fig. 5 is a flow diagram illustrating conceptual steps according to one embodiment of the invention, and fig. 4 represents a specific implementation of the flow diagram.

Description of The Preferred Embodiment

The preferred embodiment of the present invention will be described for application within a subscriber unit, such as a fixed wireless access terminal as shown in fig. 1. The preferred embodiment IS also described in IS 54-B, TDMA-3. It will be clear to those skilled in the art that this example is for illustrative purposes and that the invention may be used in other systems as well.

In fig. 1, the terminal (also called subscriber unit) comprises a radio part 10, a baseband part 60 and a voice frequency part 110. There are two interfaces between the baseband section 60 and the voice frequency section 110. The first interface, referred to as the PCM interface 175, includes digitized voice frequency Pulse Code Modulation (PCM) transmit and receive signals, while the second interface is a bi-directional serial communication interface 178. The radio section 10 and the baseband section 60 provide conversion between radio frequency and digitized voice frequency signals. The baseband section 60 is also responsible for handling the protocols associated with the RF link under the control of the voice frequency section 110.

The voice frequency section 110 includes a primary user interface including a display 120, keypad 130, reminder 150 that generates an audio reminder (e.g., ringing) and indicator that provides a visual reminder (e.g., a light indicator indicating that an extension is off-hook or an incoming call has been received), and a primary handset 140. Voice frequency unit 110 also includes a secondary user interface comprising an RJ-11 jack, and jack 230 functions as an extension jack for standard analog telephone equipment. Note that additional data jacks may be supported.

A suitable DC power supply is not shown. This may include a battery or a suitable AC power adapter or preferably a combination of both, typically powered from AC mains, with battery power as a back-up.

The ground component 10 is shown in fig. 1 as comprising a main antenna 20 connected to a radio frequency duplexer 30, the radio frequency duplexer 30 in turn being connected to a transmitter component 40 and an RF switch 35. The RF switch 35 is coupled to the receiver section 50 and selects between an input "a" of the RF duplexer 30 or an input "b" of a bandpass filter 27, which bandpass filter 27 is in turn coupled to the diversity antenna 25. Examples of such antenna arrangements are described in commonly assigned uk patent application GB 9616174.0, kitchen, by the inventor entitled "antenna arrangement", the disclosure of which is hereby incorporated by reference. However, the actual antenna arrangement is not critical to the present invention. In particular, two or more antennas may be used, which may be spatially separated, or alternatively, the received signals may have different polarizations. Furthermore, a combination of spatial and polarization diversity may be used.

Both the receiver 50 and the transmitter 40 of the radio part 10 are connected to the RF modulator/demodulator and baseband interface part 70 of the baseband part 60. The baseband section 60 also includes a suitable baseband Digital Signal Processor (DSP)80 and a suitable baseband microcontroller 90, which in turn is coupled to the T1A port 100. The T1A (test interface adapter) port communicates with a data terminal (e.g., a personal computer) using the T1A cell to set the terminal to various states and execute commands and/or procedures for testing or verification. Texas instruments TCM 4300ARCTIC (advanced RF cellular telephone interface Circuit) chip fits into component 70, while TI TDMA-3DSP fits into baseband DSP 80. Baseband microcontroller 90 IS a suitable air interface microprocessor that supports the call processing requirements of IS-54B with associated memory (e.g., RAM, ROM, EEPROM) in an extended protocol.

Most of the communication between the radio part and the baseband part takes place via the baseband interface 70. However, as can be seen, the control link labeled ANTSEL allows the baseband microcontroller 90 to trigger the RF switch 35.

In operation, communication signals are received at both the main antenna 20 and the diversity antenna 25, which are suitably filtered by the RF duplexer 30 or bandpass filter 27, respectively. The RF switch 35 determines which signal a or b is down-converted by the receiver section 50 according to a suitable diversity selection process, as discussed below.

The selected signal is down-converted to an appropriate IF signal by receiver component 50. The receiver section 50 also measures the received signal strength and sends a message to the RF demodulator and baseband interface section 70 so that the Received Signal Strength Indication (RSSI) is known in the art. The RSSI is then sent to the baseband microcontroller 90. The baseband DSP80 also determines a Bit Error Rate (BER) that is also communicated to the baseband microcontroller, which is also communicated to the baseband microcontroller. The baseband microcontroller 90 is used to process the 1-3 layers of the communication protocol stack, manage control of the RF radio section 10 and the baseband section 60, and also perform user interface functions.

The present invention is primarily concerned with how RSSI and BER measurements are used in order to determine how the RF switch 35 should be triggered in order to select which antenna to use for reception.

A diversity selection process according to one embodiment of the invention will be discussed with reference to the flow chart of fig. 2 and the timing reference shown in fig. 3. Fig. 2 IS a flowchart of the operations performed by the baseband microcontroller 90 according to this embodiment of the present invention to form an IS-54B, TDMA-3 system for supporting MAHO. For example, fig. 2 represents the steps performed according to a software program stored in the relevant memory (not shown) of the microcontroller. It should be noted that this example is described for a TDMA-3 system, where each frame has 6 time slots and each frame is divided into two half-frames, each half-frame having a receive time slot of interest to each user. In the example shown in fig. 3, 6 slots per frame (3 slots per half frame), where slots 1 and 4 are of interest to the terminal. FIG. 2 may be better understood with reference to the following definitions:

a = antenna a (main antenna);

b = antenna B (diversity antenna);

SW = RF switch 35 for selecting between a and B;

thr01= defining a suitably high RSSI level so that no switching of antenna parameters is required;

"BEST" is a variable that defines which antenna is selected as the BEST antenna for the next half frame;

RSSI _ a = RSSI value measured on antenna a; and

RSSI _ B = RSSI value measured on antenna B.

In fig. 2, step 250 represents an initialization step in which RF switch 35 is set to receive from main antenna (a)20 through RF duplexer 30. In addition, this system sets the main antenna a as the best antenna for the next half frame by default. The system will then receive data, which may be control information or voice or data from a traffic channel. After reception is complete during the appropriate time slot, e.g., time slot 1, there is a time period before the system transmits data. In this embodiment, it IS appropriate for IS-54B of a TDMA/FDD system, which IS approximately 3.7 milliseconds during this time (labeled idle A at 320 in FIG. 3). During this time, the synthesizer of receiver 50 tunes to another frequency for RSSI (received signal strength indication) measurements for Mobile Assisted Handoff (MAHO) according to IS-54B requirements, as shown in step 252 of fig. 2. This allows MAHO measurements to be made during idle times when there is no reception or transmission. This has the advantage of preventing transmit leakage through the duplexer during MAHO measurements, thus allowing absolute measurements to be made that are not affected by the transceiver's own transmissions. The system then returns the synthesizer to the receive channel frequency and triggers the RF switch to receive from the main antenna if it is not ready, as shown at step 253.

The next step, shown at 256, involves measurement of RSSI as received at antenna a. Advantageously, this step allows for the measurement of the RSSI of the receive channel, while the unit also transmits data on the transmit channel, as can be seen at 345 in fig. 3. Diversity measurements can be made during transmission because any leakage typically affects both RSSI measurements equally. Thus, the diversity selection process can use a relative measurement of two antenna RSSI, rather than the absolute measurement required by the general MAHO. However, as described in fig. 3, no measurement is made during the transmit slot on period 343 due to the instantaneous effect on one of the RSSI measurements.

To compare the RSSI between the antennas, the RF switch is triggered to select the signal originating from the diversity antenna, as shown in step 260. The RSSI value from this signal is then measured at 263. If necessary, the RF switch is reset back to the value associated with the "BEST" variable received at step 266. In other words, RSSI measurements are taken for both antennas, and then the last selected best antenna is selected for the next receive slot, and then the data is demodulated at step 268.

After the RSSI measurements are made from both antennas, both values are compared to a threshold, as shown in step 270. If both RSSI-A and RSSI-B are above the threshold thr01, both antennas receive a strong enough signal. In this case, the best value is unchanged and the system continues to receive with the current antenna. However, if RSSI-a or RSSI-B is below threshold thr01, the system compares the received signal strength from each antenna, as shown in step 280. If RSSI-A is greater than or equal to RSSI-B, the best antenna is set to A, as shown in step 285. Then, at step 287, the RSSI-A value is sent to the DSP to adjust the internal DSP Automatic Gain Control (AGC) to avoid bit glitches, which are the result of exceeding the maximum input level of the baseband demodulator. The cycle then continues in the next frame. However, if RSSI-B is greater than RSSI-a, then accordingly, as shown at steps 290 and 295, the best antenna is set to diversity antenna B and the RSSI received at the antenna is sent to the DSP before the period that the next frame continues.

As described above, and as can be seen in fig. 3, RSSI measurements at antenna a and at antenna B occur during a transmission timeslot. As described, the selection process determines which antenna is used for the next receive slot. Alternatively, given enough processing at the available time, the process may determine that the antenna is for reception during the current field. For example, referring to fig. 3, the terminal receives once every half frame (i.e., every 3 slots, such as slots 1,4,1, etc.) for a TDMA-3 system. It is best assumed that: there is sufficient time to select the best antenna during idle B before the start of slot 4. However, unless there is very fast fading, it has proven sufficient to revert to the current antenna for time slot 4, so that any change in the best antenna occurs for the next time slot (i.e., time slot 1 in the next frame).

As shown in this embodiment, if diversity RSSI measurements are made during the transmit burst, the duplexer 30 must have sufficient filtering to prevent the transceiver's own transmissions from interfering with its diversity antenna RSSI measurements. However, for systems with sufficient processing power, RSSI measurements can be made during the idle time between transmission and reception of bursts.

The advantages of the diversity selection procedure described above therefore include diversity measurements on BEST antennas used between the end of one receive slot (i.e., the slot of interest) and the beginning of the next receive slot, along with MAHO measurements. Therefore, all data in the reception slot is received using the same antenna. Thus avoiding bit glitches due to RSSI measurements or switching antennas during receive slots.

Preferably, RSSI-A and RSSI-B represent the average RSSI power level during the time that the measurements are taken. In addition, to avoid "ping-pong" between antennas, RSSI power level averaging over more than half a frame may be used. Furthermore, the switching rate may be limited by a hysteresis value M, which may take the value 1,2 … 255, to prevent switching between antennas unless the RSSI comparison is the same for M subsequent fields. These accurate representations are advantageous where fading is slow or where the demodulator is sensitive to antenna changes often. This is typically the case if the two antennas are spaced far enough apart that they see different signal path delays or where the two antennas often differ significantly in signal level. In these circumstances, hysteresis, averaging, or both may be applied.

The diversity selection process described above is particularly suited to switching antennas in order to avoid multipath fading. According to another embodiment of the present invention, the terminal may switch antennas even if the currently selected antenna has a higher average RSSI in order to improve the reception difference caused by the co-channel interference (CCI).

Fig. 4 is a flow chart of the steps performed by the baseband microcontroller according to a software program stored in the microcontroller's associated memory (not shown) according to an embodiment of the present invention that uses both RSSI and BER to determine antenna selection. In this embodiment, the diversity selection process selects which antenna to use based on testing for the presence of co-channel interference and testing signal levels. In the described embodiment, Bit Error Rate (BER) is used as part of the CCI performance test. Alternatively or in addition to measuring BER, the system may measure a Coded Digital Verification Color Code (CDVCC) parity checksum confirming that it was decoded correctly.

FIG. 4 may be better understood with reference to the following definitions:

a = antenna a (main antenna);

b = antenna B (diversity antenna);

SW = RF switch 35 for selecting between a and B;

thr01= define a suitably high RSSI level so that switching antenna parameters is not required;

"BEST" is a variable that defines which antenna is selected as the BEST antenna for the next half frame;

RSSI _ a = RSSI value measured on antenna a; and

RSSI _ B = RSSI value measured on antenna B.

"CURRENT" is a variable that defines the CURRENT antenna a or B.

"OTHER" is a variable that defines another antenna, either B or A, that is not in use.

Thr20= setting a BER threshold parameter for identifying whether the BER is normal or not.

"M" is a hysteresis parameter (hysteresis M =7 for BER, while for RSSI-based switching M =0, M =7 is chosen for BER to ensure interference persistence and absence of artifacts 0 < M < 255)

"hysteresis Cnt" is a variable used as a counter.

"CCI Hold Cnt" is a variable used as a counter.

"DF" is a flag (test purpose) used to disable a portion of the code.

"JF" is a marker used to alter the operation of the algorithm in order to adjust for different durations of interfering signals.

Thr01= -50dB (point allowing diversity (range-120 < Thr01 < -40))

Thr20= 0.5% BER (a value for determining whether the BER is normal, ranging from 0% < Thr20 ≦ 8%).

Thr21= -90dBm (above this value RSSI is considered normal, in the range-120 < Thr21 < -40).

"Z" is a parameter that defines the length of the CCI hold interval in half-frame increments.

In fig. 4, steps 402,404,406,408 represent initialization steps in which the RF switch 35 is set to receive from the main antenna (a)20 through the RF duplexer 30. In addition, the system sets the main antenna a as the best antenna for the next half frame as a default. The system then receives data, which may be control information or voice or data from a traffic channel. After reception is complete during the appropriate time slot, e.g., time slot 1, there is a time period before the system transmits data. In this embodiment, which IS suitable for being IS-54B of a TDMA/FDD system, this time period IS approximately 3.7 milliseconds (marked with idle A at 320 of FIG. 3). MAHO measurements are preferably made during this idle period, if desired. The system then returns the synthesizer to the receive channel frequency and triggers its reception from the main antenna a if the RF switch is not ready, as shown in step 420.

The next step, as shown at 423, involves the measurement of the RSSI received at antenna a. To compare the RSSI between the antennas, the RF switch is triggered to select the signal originating from the diversity antenna, as shown at step 426. The RSSI value of this signal is then measured at 429. If necessary, the RF switch is reset back to the value associated with the BEST (BEST) variable at step 432 for data reception. In other words, RSSI measurements are made for both antennas, then the last selected BEST antenna is selected for the receive slot, and then the data is demodulated in step 435. This RSSI information is saved for use at steps 452 and 465.

The following steps, including steps 439 to 449, determine whether the BER is normal. "BER normal" is a state defined based on the set of parameters and the current BER demodulated in step 435. If the BER is normal, then the selection process uses a faster RSSI-based conversion that begins at step 465 to overcome the multipath fading. If the BER is not normal, a slower conversion process based on signal quality measurements over multiple frames is started at step 452 to determine if CCI is present.

Steps 439 to 449 are used to determine whether the BER is normal. After step 439 half frame boundary, the measured BER of the previous demodulation at step 435 is compared to a threshold thr20 at step 440. If the BER is less than thr20, the "lag Cnt" is reset to zero at step 443. If not less than thr20, the hysteresis Cnt is incremented by 1. The value of the lag Cnt is then compared to M to determine if BER is normal at step 449. The inclusion of these steps 439 to 449 implements a hysteresis function such that the BER must be greater than or equal to thr20 for "M" consecutive fields before the selection process determines that the BER is not normal. This prevents incorrect decisions due to burst errors by testing only non-transient, poor BER conditions.

If the BER is not normal, a transition based on slower multiframes is initiated at step 452. Fig. 4C shows steps for implementing portions of the selection process that use the RSSI signal and BER information to determine if CCI is present. If present, the antenna switching is driven according to the BER so that another antenna may be selected, which may have a better SIR due to different multipath combinations of signal and interference.

At step 480, the current antenna RSSI is compared to thr01 to determine if the RSSI is normal. If the RSSI is normal (i.e., RSSI-current (currently) is greater than thr21), then CCI is considered present because the signal strength is good but the BER is not normal and the RSSI measurement is considered signal plus interference power. Step 486 compares the other RSSI with thro1 to determine if it is normal. If the other RSSI is normal, the operation branches to step 492 and then switches to the other antenna at step 495. The hysteresis count ccihold prevents over-triggering (toggling) between antennas by holding the selected antenna for 2 fields at step 492. This keeping of the selected antenna is achieved in conjunction with steps 455,458 and 470.

At step 486, if the result is that the other RSSI is not normal, the algorithm assumes that the transition is not beneficial. The current antenna therefore remains the best antenna (step 498) and no switch to another antenna is necessary. It is known that excessive or unnecessary triggering between antennas results in performance degradation in a general "blind handover" or "handover and hold" algorithm.

If the CURRENT RSSI is not normal at step 480, the poor BER determined at step 449 is likely due to a low signal strength of the received signal. The selection process then proceeds to step 483 where another RSSI is tested. If the RSSI of the other antenna is also not normal (i.e., below thr21), then at step 498, the antenna is still the best antenna at present. If the OTHER (OTHER) RSSI is normal, then a switch to the OTHER antenna is initiated at step 495. Optional step 489 cuts off any previously set hold by setting CCI hold Cnt =0 to provide a selective jump out of slow BER based transitions (if JF = 1). This flexibility allows for the formulation of a selection procedure for interference and signal deviations found in various propagation environments.

Referring further to step 449, if the BER is normal, a hold check is performed at step 455 to determine if the current antenna should be held due to the most recent conversion to it based on CCI. (this duration is controlled by the parameter Z). Step 458 decrements this counter every half frame for which the "hold" condition still exists.

If the CCI holds Cnt =0, then the BER is normal and there is no recent transition due to BER difference (i.e., no hold condition exists) at step 455, so RSSI-based transition is allowed for half a frame half frame to overcome multipath fading at step 465. Note that optional step 461 allows setting of the disable flag DF to disable RSSI-based switching, e.g. to allow testing only for BER-based switching.

At step 465, the conversion process based on multipath fading is started and the selection process proceeds as shown in fig. 4D.

The RSSI measurements from both antennas are compared to a threshold, as shown at step 500. If both RSSI _ a and RSSI _ B are above the threshold variable thr01, this means that both antennas are receiving a strong enough signal, and therefore no switching of antennas is required. In this case, the best value is unchanged and the system continues to receive with the current antenna. However, if either RSSI _ a or RSSI _ B is below the threshold variable thr01, the system compares the received signal strength from each antenna, as shown at step 505. If RSSI _ is now greater than or equal to RSSI _ other, then the best antenna is set to the current antenna as shown in steps 510 and 515. Optionally, the RSSI _ present value is sent to the DSP, and the internal DSP Automatic Gain Control (AGC) is adjusted to avoid bit glitches that occur when the maximum input level of the baseband demodulator is exceeded. This step is denoted as a default, since this is typically required only in the condition when the two signals from the two antennas are fading rapidly or have significant time spread between them.

The cycle then continues in the next frame. However, if the Other RSSI _ Other is greater than RSSI Current, then accordingly, as shown at steps 520 and 525, the antenna is preferably set to another antenna and optionally the RSSI received at the Other antenna is sent to the DSP. As shown at step 530, the hysteresis Cnt variable is reset to zero before continuing the loop in the next frame, since the switch to another antenna has been selected.

One advantage of the combined RSSI and BER based switching is that it automatically adjusts to different channel conditions whether the degradation is controlled by multipath fading or by CCI.

Note that the preferred embodiment of the design using a main antenna and a diversity antenna based on polarization diversity effectively provides microscopic diversity. In this case, the BER based algorithm depends on the likelihood that the multipath fading to the interference is different on the other antenna. (note that in the solid-in case, the average signal and interference levels are about the same over a period of several minutes).

An alternative embodiment of the invention is to use a remote main antenna and therefore the distance separating the main and diversity antennas is greater and therefore the BER based algorithm at the user terminal can overcome the long term poor SIR since the masked average signal and interference levels are likely to be different.

As described, the selection process determines which antenna should be used in the next receive slot. Depending on the frame structure and the processing time of the system, this may be the time slot of interest in the current (half) frame or the time slot of interest in the following (half) frame.

Fig. 5 is a flow diagram illustrating conceptual steps according to one embodiment of the invention, and fig. 4 represents a specific embodiment. For example, steps 483 and 486 determine whether RSSI _ Other is normal as a rough estimate of whether the signal quality of the Other antenna is normal. In fig. 4, this test uses another known RSSI. However, other tests such as testing BER may be best in some circumstances, particularly if additional DSP processing is available.

Step 600 represents the start of each frame. In this embodiment, the first step comprises evaluating whether the quality indication of the received signal on the current antenna has met a certain condition. Preferably this is determined by evaluating Bit Error Rate (BER), CDVCC, or both during each frame, and determining whether the quality has met the threshold in M frames. Checking the quality in M frames has the advantage of avoiding excessive transitions due to momentary drops in quality. If the test at 610 is not met, the system evaluates whether it is beneficial to select another antenna due to poor quality on the current antenna. An evaluation is made as to whether the signal received on the other antenna satisfies a second condition, as shown at step 620. The determination 620 may be made by evaluating the RSSI of the other antenna relative to an established threshold. However, in some environments there is sufficient processing available to make a determination of both the quality and strength of the other antenna. In any case, if the criterion is not met by another antenna, then the switch is not beneficial and the current antenna selection is maintained, as shown at step 660. However, if the evaluation of step 620 indicates that the other antenna does satisfy the condition, it is beneficial to select the other antenna for reception. Thus, another antenna is selected as the best antenna in step 630. A determination is made as to whether the quality difference is due to a weak signal, such as fading conditions, or whether the quality difference of another scheme is due to co-channel interference. A determination is made at step 640 by evaluating whether the RSSI satisfies a third condition, such as whether the RSSI exceeds a minimum threshold during the current frame. If the current RSSI does not meet this condition, it is clear that the quality is poor due to co-channel interference rather than poor signal strength. Therefore, a hold condition is established in step 650 to prevent subsequent switching of the selected antenna within the specified number of frames.

A determination is made as to whether a hold condition exists in order to avoid switching back to an antenna that was previously deemed to have a poor SIR. As shown in FIG. 5, a hold-in-setting evaluation is performed at step 670. Those skilled in the art will note that this hold assessment may alternatively be performed prior to step 610. In any case, if hold is set, the hold counter, which counts the number of frames since the hold condition was set, is decremented (step 680) until the hold condition no longer exists at step 685. In this case, the selection process continues at the next frame with the current antenna selected as the best antenna.

If, however, hold is not set, then at step 690 a determination is made as to which antenna is receiving a stronger signal and that antenna is selected for the next frame. The process then continues to the next frame. In the described embodiment, the quality indication (e.g., BER) is tested over "M" consecutive frames. If x of the y consecutive slots do not pass the threshold (e.g., if 3 of the 4 consecutive frames are bad, the quality is poor), then the test for the quality difference may be satisfied alternately.

Note that another antenna arrangement may be used. For example, an optional pair of remote diversity antennas may be used, which are selected using a separate RF switch depending on the external communication link from the controller.

Many modifications, variations and adaptations may be made to the particular embodiments of the invention described above without departing from the scope of the invention, which is defined in the claims.

Claims (20)

1. A diversity selection process for a transceiver system having at least two antennas, comprising the steps of:

a) selecting a previously determined best antenna as a current antenna;

b) evaluating whether a signal quality indication received at a current antenna satisfies a first condition;

c) responsive to said quality meeting said first condition, if a previously set holding condition was not met

Re-existence, selecting the antenna with greater received strength indication (RSSI)

As the best antenna for the next frame;

d) in response to the quality not satisfying the first condition:

i) assessing whether a signal received on the other antenna satisfies a second condition;

ii) in response to said further antenna signal satisfying said second condition:

A) selecting the other antenna as the best antenna for the subsequent time slot of interest; and

B) evaluating whether the received signal strength of the signal received at the present antenna exceeds a threshold,

if the threshold is exceeded, a holding condition for a prescribed number of frames is set.

2. The method of claim 1, wherein the first condition is satisfied if the quality indication of the received signal for a specified number of frames satisfies a minimum threshold.

3. A method according to claim 2, wherein the quality indication comprises a determination of one or both of a bit error rate of the received signal or an encoded digital verification color code.

4. A method according to claim 3, wherein step c) comprises the step, in response to said quality of said first condition being met:

i) assessing whether a hold condition exists on the current antenna and if so decrementing the hold

A hold counter; and

ii) in response to the absence of a hold condition, selecting an antenna with a greater RSSI as the sense

The best antenna for the subsequent time slot of interest.

5. The method of claim 3, further comprising, before step b), the steps of: it is evaluated whether a hold condition exists at the present antenna and if so, the hold counter is decremented and described above and the selection of the best antenna is not changed.

6. The method of claim 4, wherein step d) i) comprises comparing the RSSI of the signal received by said another antenna with a threshold.

7. The method of claim 4, wherein step d) i) comprises comparing the quality indication of the signal received by said another antenna with a threshold.

8. The method according to claim 1, wherein step b) comprises the steps of:

i) assessing whether the bit error rate of the received signal exceeds a threshold;

ii) in response to said threshold being exceeded, incrementing a counter, otherwise if said threshold is not exceeded

A threshold value, resetting the counter; and

iii) comparing said counter with a predetermined value, if said counter exceeds said predetermined value

A value determining that said quality indication of the signal received at the current antenna satisfies the first criterion

And (3) a component.

9. A method for diversity antenna selection for a terminal operating in a wireless communication system, comprising the steps of:

a) receiving on a previously selected current antenna during a receive timeslot;

b) testing the reception of different channels;

c) testing reception of a current channel of the current antenna;

d) testing reception of the current channel by another antenna; and

e) selecting the antenna with the best test result as claimed in claim 1

The preferred antenna.

10. A diversity selection process for a transceiver system having at least two antennas comprising the steps of:

i) determining a Received Signal Strength Indication (RSSI) received by each antenna;

ii) determining an indication of the signal quality at the present antenna;

iii) evaluating whether the quality of the signal received on the current antenna is sufficient for a defined period

Can;

iv) responsive to said evaluating step, determining that the quality is not sufficient during said period, evaluating

Whether a signal received by the other antenna satisfies a condition;

v) the condition is satisfied in response to a signal received by the other antenna;

a) selecting another antenna as a current antenna for reception during a subsequent frame; and

b) in response to the received signal strength of the signal received by the present antenna having exceeded the prescribed threshold,

the maintenance of subsequent transitions for a specified number of frames is established.

11. The method of claim 10, further comprising the step of:

vi) in response to said evaluating step, determining that the quality is sufficient for the specified period, if

Remaining unset, selecting the antenna with greater RSSI as the current day of the subsequent frame

A wire.

12. The method of claim 11 wherein the step of determining the Received Signal Strength Indication (RSSI) received by each antenna comprises measuring the RSSI of the current channel received on one antenna and then measuring the RSSI of the current channel received on the other antenna, wherein both said measuring steps occur when the transceiver is either idle or transmitting, and wherein the method further comprises the steps of tuning the transceiver to the other channel and testing reception on the other channel when the transceiver is not transmitting.

13. A wireless terminal, comprising:

a receiver;

a first antenna;

at least one alternative antenna;

a switch for selecting which antenna provides an input to said receiver; and

a controller adapted to control the switch according to the method as claimed in claim 1.

14. A wireless terminal, comprising:

a receiver;

a first antenna;

at least one alternative antenna;

a switch for selecting which antenna provides an input to said receiver; and

a controller adapted to control the switch according to the method as claimed in claim 2.

15. A wireless terminal, comprising:

a receiver;

a first antenna;

at least one alternative antenna;

a switch for selecting which antenna provides an input to said receiver; and

a controller adapted to control the switch according to the method as claimed in claim 3.

16. A wireless terminal, comprising:

a receiver;

a first antenna;

at least one alternative antenna;

a switch for selecting which antenna provides an input to said receiver; and

a controller adapted to control the switch according to the method as claimed in claim 4.

17. A wireless terminal, comprising:

a receiver;

a first antenna;

at least one alternative antenna;

a switch for selecting which antenna provides an input to said receiver; and

a controller adapted to control the switch according to the method as claimed in claim 7.

18. A wireless terminal, comprising:

a receiver;

a first antenna;

at least one alternative antenna;

a switch for selecting which antenna provides an input to said receiver; and

a controller adapted to control the switch according to the method as claimed in claim 8.

19. A wireless terminal, comprising:

a receiver;

a first antenna;

at least one alternative antenna;

a switch for selecting which antenna provides an input to said receiver; and

a controller adapted to control the switch according to the method as claimed in claim 9.

20. A wireless terminal, comprising:

a receiver;

a first antenna;

at least one alternative antenna;

a switch for selecting which antenna provides an input to said receiver; and

a controller adapted to control the switch according to the method as claimed in claim 12.