Combined spatial switch-over system

The invention relates to a telephone station with a space diversity system and a method therefor. Mobile radiotelephone arrays are becoming increasingly important in telephony and may possibly replace a significant portion of fixed wireline services as such systems become more technically efficient.

Rather, mobile telephony is based on radio frequency (RF) transmission rather than wireline technology, and is therefore faced with difficulties not encountered in wireline services.

Although mobile radiotelephone devices have been based primarily on analog technology, such a technique has serious limitations such as: Complexity, spectrum performance, secrecy and cost. This has led to developments in which digital technology, which is already being used in hard-wired telephony, replaces the existing analogue technology.

It will be apparent that the mobile telephone network will include both portable and vehicle-mounted telephone sets. Although the present invention is useful for portable device types, it primarily deals with the vehicle-mounted systems.

From DE 30 15 087 A1 a transceiver control device comprising a central processing unit and a plurality of mobile units is known. Each remote unit comprises a transceiver for transmitting and receiving RF signals to other transceivers and means for detecting the signal-to-noise ratio of the received signal. A signal is modulated according to the signal-to-noise ratio along with the received signal for transmission to the CPU. The remote unit having the best signal-to-noise ratio is selected for subsequent communication. DE 30 06 990 A1 discloses a system for automatically selecting an antenna which has the best received signal from a plurality of antennas. From US 4,704,734 a method and apparatus for determining the strongest received signal from a plurality of adjacent cellular transmitters is known. Further, US 4,214,213 discloses a system which selects the receiver of the highest quality signal from a plurality of antennas. Finally, from US 4,675,863 a system for wireless transmission of a plurality of information signals between a base station and a plurality of subscriber stations is known, the system having a single transmitting antenna.

One problem encountered with RF transmission systems, especially when such systems are used in a mobile environment, is their fading and shading sensitivity. This is a well-known phenomenon that frequently occurs in car radio reception; the reception abruptly disappears in some places, only to be restored by a small movement of the vehicle.

A well-known method for combating fading and shading is the use of multiple reception technology or diversity. Two diversity techniques have been used so far; on the one hand the time diversity consisting of the repeated broadcasting and the repeated reception of a message and on the other hand the frequency diversity consisting of transmission and reception of a message on several carrier frequencies. Both methods, however, are disadvantageous because they require additional bandwidth.

A third type of diversity, which does not require additional bandwidth, is space diversity. In the latter, two or more antennas are used, with the antennas being placed on the vehicle at an appropriate distance. In view of the fact that the fading behavior of these antennas is statistically independent of one another, it is to be assumed that fading disturbances occur in one of the antennas, with the other antenna receiving a full signal. However, the separate antennas could lead to signal doubling and interference if not properly addressed.

The present invention relates to a telephone station having a space diversity system and a method therefor, wherein the separate signals of the separate antennas are effectively combined into a single, fading and shading free signal, while avoiding duplication and interference of the individual signals, the advantages of space diversity no additional bandwidth and the benefits of other diversity techniques such. B. the time diversity or the frequency diversity are maintained.

In essence, the arrangement of the invention consists of an antenna circuit with a primary unit (or master), while the other (antenna circuit) consists of a diversity unit (or slave). Each of these units receives its own signal and handles parity errors, To detect the level of automatic gain control (AGC) and connection quality (the term "parity error" should be interpreted as meaning that a bit error causes distortion or fading, a high level of the automatic gain control (AGC) shows a deterioration of the signal, caused either by fading or interference, and the quality of connection is a measure of the phase error - the higher the quality of the connection, the lower the phase error).

The processed parity errors, link quality and automatic gain control (AGC) levels of the two antenna units are then compared, and the better signal with the fewest parity errors, the lowest AGC level and the best link quality is leaked to the receiver.

Although this space diversity arrangement is described herein in connection with the receiving side of a subscriber unit or a base station, this arrangement is also applicable in connection with the transmitter side of a subscriber unit or a land station. Further advantages of the arrangement according to the invention will become apparent from the embodiments described with reference to the following figures.

Fig. 1 is a block diagram of a post-synthesis spatial diversity arrangement of the present invention employed in the receiving section of a subscriber unit.

Fig. 2 is a block diagram similar to the diagram shown in Fig. 1, but showing a pre-synthesis spatial diversity arrangement.

Figures 3A and 3B are block diagrams of a post-synthesis type space diversity arrangement used in a land station.

Fig. 4 is a block diagram of a diversity arrangement composed of the arrangements of Figs. 3A and 3B.

Fig. 5 is a block diagram of a pre-synthesis space diversity arrangement used in the land station. <tables><table><title>GLOSSARY</title><tgroup cols="2"><thead><row><entry align="left">Acronym</entry><entry align="left">definition</entry></row></thead><tbody><row><entry align="left">AGC</entry><entry align="left">Automatic gain control (Automatic Gain Control)</entry></row><row><entry align="left">CCU</entry><entry align="left">Channel monitoring unit (Channel Control Unit)</entry></row><row><entry align="left">CODEC</entry><entry align="left">Composite Encoder and Decoder (Combined Coder and Decoder)</entry></row><row><entry align="left">DMA</entry><entry align="left">Direct memory access (Direct Memory Access)</entry></row><row><entry align="left">FIFO</entry><entry align="left">FIFO stack (first in first out memory)</entry></row><row><entry align="left">IF</entry><entry align="left">Intermediate frequency</entry></row><row><entry align="left">LQ</entry><entry align="left">Link quality</entry></row><row><entry align="left">MODEM</entry><entry align="left">Composite Modulator and Demodulator (Combined Modulator and Demodulator)</entry></row><row><entry align="left">MUX</entry><entry align="left">multiplexer</entry></row><row><entry align="left">PCM</entry><entry align="left">Pulse Code Modulation</entry></row><row><entry align="left">PE</entry><entry align="left">Parity error</entry></row><row><entry align="left">RELP</entry><entry align="left">Linear prediction of remanent excitation (Residual Exited Linear Prediction)</entry></row><row><entry align="left">RF</entry><entry align="left">High frequency (radio frequency)</entry></row><row><entry align="left">Rx</entry><entry align="left">Receive</entry></row><row><entry align="left">SOUTH</entry><entry align="left">Tunable Frequency Generator (Synthesizer Up / Down Converter)</entry></row><row><entry align="left">Tx</entry><entry align="left">Broadcasting (Transmit)</entry></row><row><entry align="left">VCP</entry><entry align="left">Voice Processor (Voice Coder Processor)</entry></row><row><entry align="left">VCU</entry><entry align="left">Voice Codec Unit</entry></row></tbody></tgroup></table></tables>

FIG. 1 shows the arrangement according to the invention applied in a subscriber unit, which is generally designated by the reference numeral 10 and includes a primary unit (or master) 12 and a diversity unit (or slave) 14th Each unit contains an antenna 16 or 18 and each antenna is connected to a radio 20 or 22 connected. Each radio is in both transmission and reception in the intercom transmission mode with a corresponding modem processor 24 or 26 and each modem processor is in intercom transmission mode via respective DMA interfaces 28 and 30 to corresponding baseband processors 32 and 34.

Each of the baseband processors is connected to a respective latch 36 and 38. Each of the base processors is also in communication with a multiplexer 40, the PCM signals being transmitted via respective lines 42 and 44 from each baseband processor to the corresponding multiplexer input; the multiplexer is further provided with a switch which is driven by the baseband processor 32 via a line 46. The multiplexer transmits its PCM output over line 48 to a CODEC 50, which communicates with a handset 52 in the intercom mode.

In operation, the audio signals broadcast by the land radio station are received in both the primary unit 12 and the diversity unit 14. These signals, which are a compression and coding by means of z. B. RELP analysis, pass from the respective antennas 16 and 18 to the respective radios 20 and 22 , which in turn transmit these signals in high frequency form to the respective modem processors 24 and 26. The modem processors demodulate the signal and transmit it in the form of demodulated symbols to the corresponding DMA interfaces 28 and 30; from this, the latter signals are leaked to the corresponding baseband processors 32 and 34.

Each of the baseband processors is provided with means which perform a RELP synthesis of the incoming compressed information at which the information is decompressed or expanded. The decompressed PCM information is then forwarded to the multiplexer 40 either via line 42 from the primary baseband processor 32 or via line 44 from the baseband processor 44 in response to the multiplexer switch position. Both baseband processors determine possible parity errors by means of a redundant error coding. Such error codes such. B. the "Hammings" coding, the "Reed-Solomon" coding and the like are well known. In the present preferred embodiment, the "Hamming" coding is used.

The spoken information is transferred via the DMA interface 28 from the modem processor 24 to the baseband processor 32; this executes the RELP synthesis and detects the connection quality, the automatic gain control (AGC) level and the parity errors of the data obtained.

The speech information is likewise dubbed by the modem processor 26 via the DMA interface 30 to the baseband processor 34; this performs the RELP synthesis and captures the data quality of the speech information, including data quality factors such as link quality, automatic gain control (AGC) levels, and parity errors. The data quality is then fed to the baseband processor 32 from the baseband processor 34 via the buffer-type latches 38 and 36.

The baseband processor 32 is programmed to compare the data quality of its own circuit, consisting of parity error, link quality, and automatic gain control (AGC) levels, with the data quality received from baseband processor 34. Thus, it chooses the best quality speech information provided by the two circuits, i. H. the speech information with the highest quality of connection, with the fewest parity errors and with the lowest level of the automatic gain control (AGC); the baseband processor 32 then actuates the switch of the multiplexer depending on the selected quality of the speech information, to connect this either to the line 42 coming from the primary unit or to the line 44 coming from the diversity unit, thus forwarding the selected data. The resulting expanded PCM signal is fed by the multiplexer via line 48 to the CODEC 50, where this signal undergoes analog conversion and is fed to the receiver portion of the handset 52.

The arrangement shown in Figure 2 is analogous to that of Figure 1, with the restriction that the arrangement represents a pre-synthesis system, wherein the selected speech signal is passed to the primary baseband processor prior to expansion and that the primary baseband processor is expanding and the Dubbing of the selected speech signal to the CODEC takes over.

The system is generally designated herein by the numeral 100 and includes a primary subscriber unit 102 and a diversity subscriber unit 104. In a manner analogous to that shown in FIG. 1 each unit has an antenna, which with 106 or 108 is designated, one with 110 or 112 marked radio, one with 114 or 116 and each respective DMA interface 118 and 120 connecting the respective MODEM processors to respective baseband processors 122 and 124.

In this embodiment, the baseband processor 124 interfaces with the baseband processor 122 via a FIFO stack 126; however, it should be noted that only the baseband processor 122 performs the RELP synthesis to expand the compressed signals. Here, the speech information is transferred from the baseband processor 124 via the FIFO stack 126 to the baseband processor 122. The latter compares the data quality, consisting of link quality, parity error and automatic gain control (AGC) level of the base band processor 124 speech information, with the corresponding own data set, selects the more compressed speech information and performs a RELP synthesis to expand the compressed speech data to a PCM Signal through. The baseband processor 122 then dubbed the resulting PCM signal to the CODEC 128; Here, the signal is converted analogously and transmitted to the receiving part of a handset 130.

The above diversity arrangement has hitherto been described only with reference to a subscriber equipment; However, it is also adaptable for use in land stations. Such a land station (in the form of a post-synthesis system) is shown in FIGS. 3A and 3B, where the arrangement is generally designated by reference numeral 200. This system 200 consists of a primary channel module generally designated 202 and a diversity channel module generally designated 204.

The module 202 consists of an antenna 206 which is coupled to a tunable frequency converter (SUD) 208 which is connected via the receiving line 212 to a modem 210. The modem is also connected to the frequency converter (SUD) 208 via a transmission line 214. The modem is coupled to the channel monitoring unit (CCU) 216, which provides the correct chronological order of the transmitted modem information.

The frequency generator of the frequency converter SUD generates oscillations, which are combined with the frequencies received in the antenna and reduced. The resulting intermediate frequency is then fed to the modem via line 212. During the transmission process, the intermediate frequencies (IF) are transmitted from the modem via line 214 to the frequency converter SUD; Here they are combined with the oscillations of the frequency generator and up converted to the passage in the antenna. In view of the fact that the frequency generator produces relatively error free oscillations, it is to be assumed that the occurring errors occur in the frequencies of the modem and the antenna output.

The structure and operation of the modem, the channel monitoring unit CCU and the corresponding components are described in detail in US Pat. Nos. 4,644,561 and 4,675,863.

The modem 210 is in communication with a VCU, indicated generally at 218, which includes a plurality of voice coding processors (VCPs), here having four VCPs numbered 1, 2, 3 and no. 4 are shown marked.

The modem 210 is connected to each VCP included in the VCU 218 via respective DMA interfaces 220, 222, 224, and 226; these direct the speech information at certain time intervals from the modem 210 to the individual VCPs of the VCU 218. The speech information is then analyzed by the corresponding primary VCP, which voice processors are programmed to determine the quality of the information, i. H. to detect the parity errors, the levels of the automatic gain control and the connection quality, and to play this quality of information bundled with the PCM signal of the diversity combining unit 228.

The same information is sent to the unit 228 from the vocoder decoder (VCU) which is generally designated 230. The VCU 230, which is identical to the VCU 218 and the diversity VCPs no. 1 , No. 2 , No. 3 and no. 4 forms part of the diversity channel module 204. A modem 232 which is similar to the modem 210 and is provided with a channel monitoring unit (CCU) 234 is in communication with a frequency converter (SUD) 236 via the receive line 238 and the transmit line 240 in a similar manner to the frequency converter 208.

The modem 232 communicates with the VCU 230 via corresponding DMA interfaces, labeled 242, 244, 246 and 248; these interfaces allow the playback of information at certain time intervals from the modem 234 to the VCU 230.

Both VCUs 218 and 230 receive from the multiplexer 252 the PCM clock signal via the clock line 254 and the gate line 256. The multiplexer 252 receives the PCM signals from the diversity unit 228 via the lines 258, 260, 262 and 264.

The diversity unit 228, which includes a plurality of VCP interface circuits, is shown in detail in FIG. Fig. 4 details the interface circuit for VCP # 1; the remaining three VCP interface circuits are only shown in general terms. All four VCP interfaces are similarly constructed and each has the circuitry shown for the VCP interface.

The with no. 1 designated VCP interface circuit consists of four respective flip-flops, which are designated by the reference numerals 302, 304, 306 and 308. The flip-flop 302 receives the connection quality and the parity error information from the VCP no. 1 the primary VCU 218, while the flip-flop 304, the connection quality and the parity error information from the VCP no. 1 the diversity VCU 230 contains. The flip-flop 306 receives the amplifier control information (AGC) from the processor VCP no. 1 the primary unit (VCU) 218, while the flip-flop 308 the amplifier control information (AGC) from the processor VCP no. 1 the diversity VCU 230 receives. The complete information of the four flip-flops is fed via a common bus 310 to the microprocessor 312, which compares the quality of the information of the primary and the diversity unit, and determines which one is preferred. The microprocessor used in this embodiment is an "Intel 8031" 8-bit microprocessor.

The preferred data quality is used to generate a control signal which operates a switch of the circuitry 314 in one of the two switch positions, a switch position for receiving the PCM signal from the primary VCP no. 1 via line 316, and another switch position for receiving the PCM signal from diversity VCP no. 1 via the line 318. The selected PCM signal is output from the circuitry 314, via the channel 258 (also in FIG. 3A and 3B) to the multiplexer 252. The multiplex 252 is part of the land station. This land radio station will not be described further here since such base stations are already described in detail in US Pat. Nos. 4,777,633 and 4,779,262.

The VCP interface circuits # 2, # 3, and # 4 are all identical to r interface circuit # 1, and are interconnected to bus 310 with their PCM outputs made up of corresponding channels labeled 260, 262, and 264 ( these are also shown in Figs. 3A and 3B).

The above arrangement has been described in the context of data reception; the arrangement can also be used in the transmission area, where it works in a similar but reversed manner. If one antenna has a better reception than the other, it would also ensure a higher transmission quality because the antenna has the same appearance as e.g. As shading, etc. both receiving and broadcasting is suspended.

Fig. 5 shows a pre-synthesis land station, generally designated 400; the array consists of a primary module labeled 402 and a diversity module labeled 404. Each module is equipped with an antenna labeled 406 and 408, respectively. Each of these antennas is coupled to a radio, labeled 410 and 412, respectively, and each wireless is connected to a respective modem 414 and 416.

Each modem is connected to a plurality of DMA interfaces, four of which are shown in the present embodiment; the interfaces of the primary channel module are denoted 418, 420, 422 and 424, and the interfaces of the diversity channel module 426, 428, 430 and 432. Each DMA interface is connected to a corresponding VCP processor of the type shown in FIG. 3A and 3B, with the processors located in the primary channel module labeled 434, 436, 438, and 440 and with the processors located in the diversity channel module labeled 442, 444, 446, and 448.

The VCPs 434-440 of the primary channel module communicate with corresponding FIFO stacks labeled 450, 452, 454 and 456, while the VCPs 442-448 of the diversity channel module communicate with the same FIFO stacks.

The primary VCPs are programmed to provide an additional compare function, comparing the own data quality, consisting of link quality, parity error and automatic gain control (AGC) level, with the data quality of diversity VCPs, and a RELP synthesis (expansion). to perform the preferably compressed speech information. The resulting PCM information is fed via channels 460, 462, 464 and 466 to the multiplexer (not shown).

In addition to the above functions, the arrangement proves to be advantageous because when not working antenna caused z. B. by lightning, the activation of the other antenna is done automatically.

Although the present arrangement has been described in connection with two antenna modules, it is possible to use more than two modules, with the highest quality signal from the antennas being selected by the primary unit to provide PCM information. This arrangement would include a primary antenna unit and a plurality of diversity antenna units, and would be particularly suitable for land stations.

Furthermore, it is also possible to use a plurality of antenna systems, each consisting of a primary and one or more diversity units, with the primary unit of the system as the master of the entire network on the selected signal crucial. Such a solution would be particularly suitable for land stations.