PT92892B - COMBINATION SPACE DIVERSITY SYSTEM - Google Patents

Abstract

The invention relates to a spatial diversity system for digital mobile telephone networks which comprises at least two antennas, one antenna being part of a primary (or master) unit and the other being part of a diversity (or slave) unit, each unit having processing means to detect the "quality" of digital audio signals received by their respective antennas, the "quality" comprising link quality, automatic gain control level and parity errors; the primary unit being capable of comparing the "quality" of the audio signals received by each antenna, selecting the higher "quality" signal and transmitting the higher "quality" signal to the telephone network. <IMAGE>

Description

INTERNATIONAL MOBILE MACHINES CORPORATION "COMBINATION SPACE DIVERSITY SYSTEM"

BACKGROUND OF THE INVENTION

Cellular (or mobile) telephone systems are assuming an increasing importance in the telephone technique, and may eventually divert a significant portion of the fixed service by wired circuit, when it becomes technically more efficient. Cellular telephony relies on radio frequencies (RF) instead of wired transmission technology and is therefore subject to many problems that do not arise in wired telephone service.

Although mobile cellular systems have hitherto been based primarily on analogue technology, this technology has severe limitations involving, among other things, complexity, spectrum efficiency, privacy and costs. This has led to developments in which digital technology, which already has a fixed place in the telephone service, is now replacing analogue technology. It is clear that mobile systems will eventually include either a portable or hand-held telephone or a vehicle-mounted telephone. The present invention, although predictably adaptable to the portable type, relates mainly to the type of system mounted on a vehicle.

One of the problems with PR-based communication systems, especially when used in the mobile environment, is their susceptibility to signal fading and the shadow effect. This is a common phenomenon that is often found in a radio mounted on a vehicle, according to which the reception suddenly weakens in a restricted area but is restored after a small displacement of the vehicle.

A well-known technique for combating these fading and shadowing effects is to use diversity processes. So far, two types of diversity have been used, diversity over time, which comprises the sending and receiving of the same message more than once, and the frequency diversity comprising the sending and receiving of a message on more than one carrier frequency. . However, both of these processes have the disadvantage that they require additional bandwidth.

A third type of diversity, which does not require this additional bandwidth, is space diversity. This comprises the use of two or more antennas separated from each other, at an appropriate distance, on the vehicle. As the fading characteristics of these antennas are statistically independent, when one is subject to fading the other can generally transmit the complete signal, thus obviating the effects of fading. However, these separate antennas provide separate signals that can lead to duplication and mutual interference, if not properly controlled.

SUMMARY OF THE INVENTION The present invention comprises a system with space diversity in which the individual signals from the separate antennas are combined effectively to produce a single high quality signal, without fading, without shadow effect, thus avoiding the duplication and interference of the signals but maintaining the advantages of space diversity, namely the non-need to use additional bandwidth, which is necessary in other diversity systems, such as time diversity or frequency diversity.

Essentially, in the system according to the present invention, one antenna circuit comprises a primary (or director) unit while the other comprises a diversity (or directed) unit. Each unit receives its individual signal and processes it to detect parity errors, the level of automatic volume control and the quality of the connection circuit (the expression "parity error" means a bit error that causes distortion or fading, iam level of automatic volume control indicates signal deterioration due to both fading and interference and the quality of the connection circuit is a measure of the phase error - the higher the quality index of the lower connection circuit will be the phase error)

The parity errors, the quality of the connection circuit and the level of automatic volume control processed from the two antenna units are then compared, being the best signal, which contains the least number of parity errors, the level of automatic control. lower volume and better quality of the connection circuit, which is applied to the receiver.

Although this space diversity system is described here as being applied to the receiving side of a subscriber unit or base station, it is also applicable to the sending side of either the subscriber unit or the base station.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block scheme of a space diversity system with post-synthesis, which realizes the present invention, used for reception in a subscriber unit; Fig. 2, is a diagram similar to that of fig. 1, but representing a space diversity system with pre-synthesis;

Figs. 3A and 3B include a block diagram of a space diversity system of the type with post-synthesis, which is used in a base station. Fig. 4 is a block diagram of the diversity combination unit used in the system of figs. 3A and 3B. - 5 - f Fig. 5 is a block diagram of a space diversity system with pre-synthesis used at the base station.

GLOSSARY OF ACRONYMS

Acronym

Definitions

AGC CCU CODEC DMA PIPO IP LQ MODEM MUX PCM PE RELP RP Rx SUD "Automatic Gain Control" &quot; Channel Control Unit &quot; &quot; Combined Goder and Decoder &quot; &quot; Direct Memory Access &quot; &quot; Pirst-in Pirst-out Memory &quot; &quot; Intermediate Frequencies &quot; &quot; Link Quality &quot; Combined Modulator and Demodulator &quot; &quot; Multiplexer &quot; &quot; Pulse Code Modulation &quot; &quot; Parity Error &quot; &quot; Residual Exited Linear Prediction &quot; "Radio Prequency" &quot; Receive &quot; &quot; Synthesizer Up / Down Converter &quot;

Automatic volume control

Channel control unit

Encoder-Decoder

Direct memory access

First-come, first-served memory

Intermediate frequencies

Connection joint quality

Modulator-demodulator

Multiplexer

Encoded pulse modulation

Parity error

Residual linear prediction comes out of

Radio frequency

Reception

Synthetic elevator / down converter - 6 - - 6 - Acronym Tx &quot; Transmit &quot; VCP &quot; Voice Coder Processor &quot; VCU "Voice Codec Unit"

Definitions

Emission

Telephone signal encoder processor

Telephone CODEC unit

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 illustrates the present invention applied to a subscriber unit, generically referred to as (10), and comprises a primary (or director) unit (12) and a diversity (or directed) unit (14). Each unit includes an antenna, respectively (16) and (18), each antenna being connected to a radio (20) and (22), respectively. Each of the radios is in two-way communication, for transmission and reception, with a MODEM processor (24) and (26), respectively, with each MODEM in bilateral combination, through the respective DMA interfaces (28) and (30) , with respective baseband processors (32) and (34).

Each of the baseband processors is in combination with a respective retainer (36) and (38). Each baseband processor is also in communication with a multiplexer (40), as indicated in (42) and (44), respectively, thus being applied the encoded pulse modulation (PCM) signals of each baseband processor to the multiplexer, which includes a switch that is controlled over the line (46) by the baseband processor (32). The multiplexer applies its PCM output, through the line (48), to a CODEC (50), which is in bidirectional communication with the handset at (52).

In operation, when audio signals are received from the base station, they are received by either the primary unit (12) or the diversity unit (14). These signals, which have been compressed and encoded, for example by RELP analysis, pass from the respective antennas (16) and (18) to the respective radios (20) and (22), which transfer them, as RF signals, to the processors respective MODEMs (24) and (26). MODEM processors demodulate the signals and transmit the demodulated symbols to the respective DMA interfaces (28) and (30), from where they are transferred to the respective baseband processors (32) and (34).

Each of the baseband processors is provided with means to perform the RELP synthesis on the compressed input data, so that the data is decompressed or expanded. The uncompressed data (PCM) is transferred, selectively, either through the line (42) of the primary baseband processor (32) or through the line (44) of the baseband processor (44) to the multiplexer (40), depending on the position of the multiplexer switch.

The two baseband processors also work to detect parity errors through error-coding. There are several forms of coding for detecting errors known in the art,

such as, for example, the encoding of "Hamming", the encoding of "Reed-Solomon" and other similar ones. In the present preferred x-embodiment, "Hamming" encoding is used.

The telephone signal data from the MODEM processor (24) are transmitted, through the DMA interface (28), to the basic band processor (32), which works in order to perform the RELP synthesis and detect the quality of the data junction. connection level, automatic AGC volume control level and parity errors in this data.

The telephone signal data from the MODEM processor (26) are also transmitted, via the DMA interface (30), to the basic band processor (34), which works to perform the RELP synthesis and to detect the quality data, which include the quality of the link junction, the level of automatic AGC volume control and the parity errors in that telephone signal data. The quality data from the baseband processor (34) is then transmitted, through the retainers (38) and (36), which act as buffer circuits, to the baseband processor (32). The baseband processor (32) is programmed to compare the quality data containing the parity errors, the quality of the link junction and the AGC of its own circuit with those received from the baseband processor (34). This processor chooses the data from the telephone signals with the best quality, that is, those that have the highest quality of the connection junction, the lowest number of parity errors and the lowest level of - 9 - AGC, of the two circuits and , through line (46), uses the quality data chosen to actuate the switch in the multiplexer to connect the multiplexer, or the line (42) coming from the primary unit, or the line (44) coming from the diversity unit to use the telephone signal data from the chosen circuit. The resulting expanded PCM signal from the multiplexer passes, through the line (48), to the CODEC (50), where it is transformed into an analog signal and passes to the receiving side of the handset (52). The system shown in fig. 2 is similar to that of fig. 1, except that it represents a pre-synthesis system, in which the selected telephone signal is transmitted to the primary baseband processor before it is expanded, then expanding the primary baseband processor and transmitting the selected telephone signal for CODEC.

Here the system has the generic designation (100) and comprises a primary subscriber unit (102) and a diversity subscriber unit (104). Analogously to the system of fig. 1, each unit comprises an antenna, respectively (106) and (108), a radio, respectively (110) and (112), a MODEM processor, respectively (114) and (116), each in bidirectional communication with the corresponding radio, and a DMA interface, respectively (118) and (120), connecting the respective MODEM processor with the respective baseband processor, (122) and (124).

In this form, the baseband processor (124) is in communication with the baseband processor (122) through a PIPO memory (126), but only the baseband processor (122) performs RELP synthesis to expand the signals pills. In this regard, the telephone signal data passes from the basic band processor (124), through the PIPO memory (126) to the basic band processor (122). The latter compares the quality data, which includes the quality of the connection junction, parity errors and the AGC level, in the telephone signal data from the basic band processor (124) with its own analog data and then takes the data. better compressed data and performs the RELP synthesis on them to expand the compressed data of the telephone signal to obtain a PCM signal. Paz then pass the resulting PCM signal to the CODEC (128) where it is converted into an analog signal which then passes to the handset receiving part (130). The diversity combining system has been described above with reference to the subscriber station, but it can also be adapted for use at the base station. Such a system for the base station (in the form of a post-synthesis system) is shown in figs. 3A and 3B, where it has the generic designation (200). This system (200) comprises a primary channel module (202) and a diversity channel module (204). The module (202) comprises an antenna (206) coupled to a synthesizer lift / lower converter (SUD) (208) that is in communication with an M0DEM (210), through a receiving line (212). The M0DEM is also in communication with the SUD (208), through the line (214) for transmission. The MODEM is coupled to a channel control unit (CCU) (216), which works to transmit data from MODEM to the appropriate time bands. The SUD synthesizer provides oscillator frequencies that are combined with frequencies received from the antenna and converted to lower frequencies, which are then passed to MODEM over the line (212). When emitted, the IP frequencies from MODEM are routed through the line (214) to the SUD, where they are combined with the frequencies of the synthesizer's oscillator and converted into higher frequencies to pass to the antenna. In any case, as the oscillator frequencies are relatively error free, any errors that appear are admitted to be those found in the frequencies of the antenna or MODEM output. The structure and operation of MODEM, CCU and its associated elements are described more fully in US patents IP 4 644 651 and IP 4 675 863, the descriptions of which are included here by reference. The MODEM (210) is in communication with a telephone CODEC unit (VCU), with the generic reference (218), which comprises a number of telephone CODEC processors (VCP), here in number of four, and designated as primary VCP ( IP 1), (IP 2), (IP 3) and (IP 4). The MODEM (210) is in communication with each VCP in the VCU (218) through DMA interfaces, designated respectively - (220), (222), (224) and (226), which act to pass the telephone signal data by the respective MODEM time bands (210) for the individual VCPs in the VCU (218). This telephone signal data is analyzed by the respective primary VCP, which are programmed to determine the quality data that comprise parity errors, AGC levels and the quality of the connection junction and to forward these quality data, together with the PCM , for the diversity combining unit (228). The same type of data is transmitted to the unit (228) from the VCU, with the generic designation (230). VCU (230), which is identical to VCU (218) and comprises diversity VCP (NS1), (N92), (N23) and (N94), is part of the diversity channel module (204). A MODEM (232), analogous to MODEM (210) and having a channel control unit (234), is in communication with an SUD (236), similar to the SUD (208), through the receiving line (238) and the emission line (240). The MODEM (232) is in communication with the VCU (23O) through DMA interfaces, respectively (242), (244), (246) and (248), which act to pass data through the respective MODEM time bands. (234) for the VCU (230).

Both VCUs (218) and (230) receive their PCM time allocation from the multiplier (252) via the clock line (254) and the port line (256). The multi-plexer (252), in turn, receives the PCM signals from the diversity combining unit (228) via lines (258), (260), (262) and (264). The diversity combining unit (228), which comprises a number of VCP interface circuits, is shown more fully in fig. 4. This figure shows the interface circuit for the VCP NSl in detail, however showing the other interface circuits for the VCP only generically. However, all four VCP interface circuits are the same, each having the specific circuits represented for the VCP NS1 interface circuit.

Looking at the VCP NSl interface circuit, there are four seals, respectively (302), (304), (306) and (308). The retainer (302) receives the quality of the link junction and parity errors from the VCP NS1 of the primary VCU unit (218) while the retainer (304) receives the quality data of the link junction and parity errors from the primary VCU unit (218). VCP N21 of the diversity VCU (230). The retainer (306) receives the AGC data from the VCP N21 of the primary VCU (218), while the retainer (308) receives the AGC data from the VCP NS1 of the diversity VCU (230). All data from the four retainers are sent via a common omnibus line (310) to a microprocessor (312) that compares the primary quality and diversity data and de-determines which are preferable. The microprocessor used in this embodiment is an 8-bit "Intel 8031" microprocessor, manufactured by Intel Corp. from Santa Clara,

California - 14 -

Preferred quality data is used to provide a control signal that oscillates a switch on the switch device (314) to one of two positions, one that receives the PCM signal from the primary VCP NS1, through the line (316), and another which receives the PCM signal from the VCP N21 of diversity through the line (318). The chosen PCM signal is sent from the switching device (314), through the channel (258) (also shown in Figs. 3A and 3B) to the multiplexer (242). The multiplexer (252) is part of the base station. This base station is not described here, but is of the type shown in United States patents NS 4,777,633 and NS 4,779,262, both of which are incorporated herein by reference.

The VCP (N92), (N23) and (N24) interface circuits, all identical to the interface circuit (N21), are connected in common to the omnibus line (310) and provide PCM outputs on the respective channels (260), (262) and (264) (also shown in Figs. 3A and 3B). The system has been described above with respect to data reception; but it can also work in a similar way, but inverse, when it is emitted. In this regard, if one of the antennas provides better reception than the other, it will also provide better emission, since the other antenna is subject to the same shadow effect, etc., for both reception and emission. Fig. 5 represents a base station system with pre-synthesis, with the generic reference (400), comprising a primary module (402) and a diversity module (404). Each of them has an antenna, respectively (406) and (408). Each of these antennas is coupled to a radio (410) and (412), respectively, and each radio is in communication with a MODEM, respectively (414) and (416).

Each MODEM is in communication with a certain number of DMAs, in this case with the references (418), (420), (422) and (424), in the primary channel module and (426), (428), (430) and (432) in the diversity channel module. Each DMA is in communication with a respective VCP of the type represented in fig. 3A and 3B, with the designations (434), (436), (438) and (440) on the primary channel module and (442), (444), (446) and (448) on the primary channel module diversity.

The VCPs (434) to (440) of the primary channel module are in communication with the respective PIPO memories (450), (452), (454) and (456), while the VCPs (442) to (448) of the module diversity channels are also in communication with PIPO memories.

The primary VCPs are programmed to provide an additional comparison function, whereby they take their own quality data that comprises the quality of the link junction, parity errors and AGC level plus that of VCP diversity, comparing the two sets quality data and perform RELP (expansion) synthesis on preferred compressed phone data.

The resulting PCM data is applied, through channels (46O), (462), (464) and (466), to the multiplexer (not shown).

In addition to the previous functions, an advantage - 16 - - 16 -

of this system is that if one of the antennas becomes non-operational, for example if it undergoes an atmospheric discharge or is damaged by any other reason, a switch is automatically made to the other antenna.

Although this system was previously described with reference to two antenna modules, it is possible to use more than two, the best quality signal of each antenna being chosen by the primary unit to provide the PCM data. This would make a primary antenna plus a number of diversity antenna units, which would be feasible especially for the base station. It is also possible to use a number of antenna systems, including each unit or several units of diversity, with the primary unit of a system acting as the director of the entire network to make the choice of signals to use. All of this would be especially achievable for the base station.

Claims (9)

CLAIMS 1.- Space diversity system for radio telephone systems, characterized by comprising: several antenna units including a primary unit and at least one diversity unit, each with an antenna; each unit having means to determine the quality data, which comprise the quality of the connection circuit, the level of automatic gain control and the parity errors of an initial audio signal; means for comparing the quality data of the diversity unit with the quality data of the primary unit; means for selecting the audio signal that has the preferred quality data; and 18- means for transmitting the selected audio signal to the telephone system. 2. Space diversity system according to claim 1, characterized in that the initial audio signals are transmitted to said antenna units from the *** # their respective antennas. 3. Space diversity system according to claim 1, characterized in that the initial audio signals are transmitted from said antenna units to their respective antennas. 4.- Space diversity system according to claim 1, characterized in that the antennas are receptive to compressed digital audio signals and that each unit has means to synthesize and expand the signals received from its respective antenna. 5.- Space diversity system according to claim 1, characterized in that the antennas are receptive to compressed digital audio signals but only the primary unit has means to synthesize and expand the compressed signals and transmit them to the system telephone. -19- 6. Space diversity system according to claim 1, characterized by being applied to a subscriber station. 7. - Diversity, space system according to claim 1, characterized in that it is applied to a base telephone station. 8. - Space diversity system according to claim 1, characterized in that the primary unit is in operative communication with a switching means, using said primary unit the quality data to operate the switching means to form a path for the audio signal selected from the primary unit to the telephone system. 9. Space diversity system according to claim 8, characterized in that said selected audio signal is transmitted by said path to a multiplexer from which it passes to the telephone system. Lisbon ,, January 18th, 1990 The Official Industrial Property Agent -20- SUMMARY "COMBINATION SPACE DIVERSITY SYSTEM" The invention relates to a system with space diversity for digital cellular telephone networks that comprises at least two antennas, making an antenna part of a primary unit (director) and the other part of a diversity unit (directed), having each of the units processing means to detect the "quality" of the digital audio signals received by the respective antennas, including "quality" the quality of the connection circuit, the level of automatic gain control and parity errors, the primary unit being able to compare the "quality" of the audio signals received by each antenna, select the signal with the best &quot; quality &quot; and transmit the signal of "better quality" to the telephone network. -21- -21- 12, ΙΟ r— '1—. η -11 — ί I________J I________J Lisbon, January 18, 1990 Agent Oíicicl cia Industrial Property