A RADIO TRANSCEIVER SYSTEM

Abstract: The invention relates to the realization of frequency hopping in radio transmitter, receiver or transceiver systems. In the system according to the invention, a separate fixed-frequency radio transmitter or radio receiver (6a to 6c) is provided for each frequency utilized in the frequency hopping. The frequency hopping is realized by switching (5) received inbound signals or outbound signals (8a to 8c) as baseband signals to the different fixed-frequency transmitters or receivers (6a to 6c) in accordance with a frequency-hopping sequence.

Description: A radio transceiver system The invention relates to the realization of frequency-hopping in radio transmitter systems, radio receiver systems and radio transceiver systems. The specifications of the European mobile radio system GSM (General Systeme Mobile) define a so- called frequency-hopping function in which the trans¬ mitting frequency during signal transmission and cor- respondingly the receiving frequency at the receiving end is varied continuously by using a suitable number of frequencies, e.g. four predetermined frequencies. Frequency-hopping has two advantageous effects, viz. frequency diversity and interference diversity. Fre- quency diversity improves the quality of a radio link mainly in cases where the radio transmitter and the radio receiver move slowly with respect to each other. If the frequency of a radio link in a digital mobile radio system is varied sufficiently from one channel time slot to another, fading situations imposed on different channel time slots do not cor¬ relate with each other, and so the time slot inter¬ leaving utilized in the system also helps to improve the quality of transmission at the reception when fading occurs. The interference diversity effect is based on the fact that the frequency-hopping sequences of base stations using the same or adjacent frequencies are different or at least at different phases with respect to each other, whereby the frequencies interfering with each other also vary from one time slot to another, and the effect of severe sources of interference is divided between several radio links, and so the effect of the inter¬ ference on an individual link is reduced. The object of the present invention is to provide a radio system realizing such a frequency- hopping function. This is achieved by means of a radio transmitter system according to the invention, which system comprises means for transmitting at least one signal at least at two transmitting frequencies varying in accordance with a predetermined frequency- hopping sequence. The system is characterized in that it comprises a fixed-frequency radio transmitter for each transmitting frequency, and means for switching said at least one signal as a baseband signal from baseband signal processing stages to said fixed-frequency radio transmitters in accordance with said frequency-hopping sequence. The invention is also concerned with a radio receiver system which comprises radio receiving means for receiving at least one signal at least at two receiving frequencies varying in accordance with a predetermined frequency-hopping sequence. The system is characterized in that it comprises a fixed-fre¬ quency radio receiver for each receiving frequency, and means for switching said at least one received signal as a baseband signal from said fixed-frequency radio receivers to baseband signal processing stages in accordance with said frequency-hopping sequence. The invention is further concerned with a radio transceiver system which comprises radio transceiver means for transmitting at least one outbound signal at least at two transmitting frequencies varying in accordance with a predetermined frequency-hopping sequence and for receiving at least one inbound signal at least at two receiving frequencies varying in accordance with said frequency-hopping sequence. The system is characterized in that it comprises a fixed-frequency radio transceiver for each pair of transmitting and receiving frequencies, and means for switching said at least one outbound signal as a baseband signal from baseband signal processing stages to said fixed-frequency transceivers and for switching said at least one received inbound signal as a baseband signal from said fixed-frequency trans¬ ceivers to the baseband signal processing stages in accordance with said frequency-hopping sequence. The basic idea of the invention is that a separate dedicated fixed-frequency transmitter or receiver is provided for each transmitting or re¬ ceiving frequency, and the frequency hopping is carried out by switching baseband signals. For instance, the frequency of an outbound signal is caused to hop in accordance with a predetermined hopping algorithm by switching a baseband signal to the different transmitters in sequence. Signals from the fixed-frequency transmitters are combined to a transmitting antenna by a combiner means. The invention offers a solution to a serious problem associated with the realization of frequency hopping in the GSM system in particular. According to the frequency-hopping algorithm the base station of. the system has to change frequency of the radio link twice within each signal frame. Since the base station transmits the TDMA frame in each time slot, it is necessary that the transmitting frequency can be changed during a guard interval, about 30 μs, be¬ tween the time slots. The frequency synthesizers of the transmitters and the combiner means combining the transmitting signals to a common antenna must also have enough time to adapt in a timed relationship with the frequency-hopping algorithm if variable-fre¬ quency transmitters are used. In practice, however, the realization of variable-frequency transmitting filters in particular in such a way that they are sufficiently rapid and economical is very difficult. The realization of the combiner means without trans¬ mitting filters or by means of broadband transmitting filters results in complicated constructions and high signal attenuations. When using fixed-frequency radio transmitters according to the invention, the trans¬ mitting filters can also be fixed, thus avoiding the above-mentioned problem. Furthermore, the construc- tion of the fixed-frequency transmitter (frequency synthesizer) is simpler and more advantageous than that of the variable-frequency transmitter. The same applies to the receiver. The invention will now be described in greater detail by means of an embodiment with reference to the attached drawing, in which Figure 1 shows a block diagram of a transceiver system according to the invention; Figure 2 shows a block diagram of the principal features of the baseband units 7a to 7c shown in Figure 1; and Figure 3 illustrates the multiplexing of time- multiplexed serial buses 8a and 9a shown in Figure 1 into the transmitting and receiving directions. Frequency-hopping according to the invention can be applied in any radio system comprising several radio transmitters, radio receivers or radio trans¬ ceivers. It is, however, especially suitable for use in cellular digital mobile radio systems, such as the GSM mobile radio system, for realizing frequency hopping in radio communication between base stations and mobile radio stations (e.g. mobile telephones). Figure 1 shows a block diagram of a transceiver system according to the invention. The system comprises at least two, preferably four, transceiver units 6a, 6b and 6c. In the GSM system, each transceiver is full-duplex, and the duplex spacing between its receiving and transmitting RF frequencies is 45 MHz. The frequency range utilized by the system is preferably from 800 to 1,000 MHz. The transceivers 6a to 6c have mutually different fixed transmitting and receiving frequencies. Outputs 10a to 10c in the transceivers 6a to 6c are connected to a radio- frequency combiner means 1, which combines the transmitters of the transceivers 6a to 6c to a common transmitting antenna 2 and the receivers to a common receiving antenna 3. Alternatively, there may be provided two receiving antennas if diversity reception is used. The radio-frequency combiner means 1 contains a bandpass-type transmitting filter for the transmitter of each transceiver unit 6, the filter being tuned automatically or manually to the transmitting frequency of the particular transmitter. Correspondingly, the combiner means 1 contains a re- ceiving filter for the receiver of each transceiver unit 6, which filter separates from the antenna signal a signal in the band of receiving frequencies and then amplifies it and divides it to all the receivers. The system of Figure 1 further comprises several baseband signal processing units 7a, 7b and 7c, which generate baseband modulating signals for the transceiver units 6a to 6c and which process the signals received and converted to the baseband fre- quency by the transceivers. A cross-point type switching matrix 5 is provided between the trans¬ ceiver units 6a to 6c and the baseband signal processing units 7a to 7c. This matrix switches the baseband transmitting signals generated by the baseband signal processing units 7 to the different transceivers 6a to 6c in accordance with a pre¬ determined frequency-hopping sequence in such a way " that the transmitting frequency of a signal generated by a certain baseband signal processing unit 7 hops from one transmitting frequency to another. Cor¬ respondingly, the switching matrix 5 switches the signals received and converted to the baseband fre¬ quency by the transceivers to the baseband signal processing units 7a to 7c in accordance with said predetermined frequency-hopping sequence. In the preferred embodiment of the invention, the signal to be transmitted is a serial time- division multiplexed digital signal comprising several, preferably eight, channel time slots. Figure 2 shows the principal functional blocks of the signal processing units 7a to 7σ of Figure 1 for the digital signal described above. The baseband processing of the signals takes place entirely in the units 7a to 7c. Generally speaking, data to be transmitted is coded and placed in a frame structure of the signal in the baseband signal processing units 7a to 7c. At the reception, the data is demodulated, the frame structure is disassembled, and decoding is carried out. More precisely, data (e.g. speech) from other parts of the radio system, such as the base station controller in the GSM system, is processed by a channel coding unit 71 before transmission. The chan¬ nel coding unit 71 may perform e.g. the following functions: adaptation of transmission rate, channel coding, interleaving, encryption, assembly of TDMA frame and adjustment of transmitter power control. Within each time slot, the unit 71 transmits a burst containing the data to be transmitted in this par¬ ticular time slot to an interface unit 74. The inter- face 74 converts the parallel data received from the unit 71 into serial form and transmits it in serial form through the switching matrix 5 to the particular transceiver 6a to 6b, the matrix 5 switching the serial base band signal in a corresponding time slot to one of the transceivers in accordance with the frequency-hopping algorithm. Correspondingly, the interface 74 receives a serial signal from a bus 8 within each receiving time slot, the serial signal containing baseband samples derived from the signal received by a transceiver 6a to 6c selected by the switching matrix 5 in accordance with the frequency- hopping algorithm. The interface 74 applies these samples in parallel form to a demodulator 73, which processes the samples. The demodulator 73 contains e.g. the following functions: sample buffering, decryption, GMSK demodulation. The demodulator 73 applies the demodulated data to a channel decoding unit 72, which performs e.g. the following functions: combining signals from different antennas when antenna diversity is used (two receiving antennas), disassembling the frame structure, breaking up interleaving, convolution decoding, block decoding, checking CRC and error correction, adaptation of transmission rate. The channel decoding unit 72 transmits the decoded data further to the other units, and, for instance, to the base station controller of the GSM system when the transceiver system is located at the base station. In the preferred embodiment of the invention, a modulator corresponding to the demodulator 73 is provided in each transceiver 6a to 6c, in which the data to be transmitted is modulated and converted up to an appropriate radio frequency. Correspondingly, the data received at the reception is converted by the transceiver down to a baseband frequency and pre- processed for demodulation. Demodulation does not take place until in the units 7a to 7c. In addition, " each transceiver 6a to 6b comprises a unit cor¬ responding to the serial interface unit 74 for receiving the serial signal through the switching matrix 5 from the baseband unit 7a to 7c coupled to it at each particular moment and, correspondingly, for transmiting a serial signal to the same baseband unit. As already mentioned above, each baseband signal processing unit 7a to 7c has a corresponding bidirectional serial bus 8a to 8c, which connects it to a respective port in the switching matrix. Similarly, each transceiver 6a to 6c is connected by a separate bidirectional serial bus 9a to 9c to a respective port in the switching matrix 5. Thus a bidirectional time-division digital connection is established between each signal processing unit 7 and the particular transceiver coupled to it in accordance with the frequency-hopping algorithm through the switching matrix 5. Preferably, the base¬ band signal processing units 7a to 7c are coupled to a new transceiver after each transmission or reception of a channel time slot during the guard intervals between the channel time slots. Bi¬ directional means that the same bus is used at dif¬ ferent times for both transmission-direction and reception-direction time slots. A time slot complying with the GSM specification may be divided into several shorter time windows for the management of this serial bus, the windows being allocated to transmission (Tx), reception (Rx) and testing (test), as shown in Figure 3. The illustrated time division of this serial connection is possible due to the fact that the transmitting and receiving moments of the GSM system . are not simultaneous. Such serial bidirectional transmission between the units 7a to 7c and 6a to 6c is simpler and more advantageous as com¬ pared with a parallel bus, in addition to which it reduces the need for cable laying as the same bus is utilized in both transmission and reception direction and simplifies the realization of the switching matrix 5. The attached drawings and the description related to them are only intended to illustrate the present invention. In their details, the systems according to the invention may vary within the scope of the accompanying claims.

Claims: Claims : 1. A radio transmitter system comprising means (6a to 6c) for transmitting at least one signal at least at two transmitting frequencies varying in accordance with a predetermined frequency-hopping sequence, c h a r a c t e r i z e d in that the system comprises a fixed-frequency radio transmitter (6a to 6c) for each transmitting frequency, and means (5) for switching said at least one signal as a baseband signal from baseband signal processing stages (7a to 7c) to said fixed-frequency radio transmitters (6a to 6c) in accordance with said frequency-hopping sequence. 2. A radio receiver system comprising means (6a to 6c) for receiving at least one signal at least at two receiving frequencies varying in accordance with a predetermined frequency-hopping sequence, c h a r a c t e r i z e d in that the system com¬ prises a fixed-frequency radio receiver (6a to 6c) for each receiving frequency, and means (5) for switching said at least one received signal as a baseband signal from said fixed- frequency radio receivers (6a to 6c) to baseband signal processing stages (7a to 7c) in accordance with said frequency-hopping sequence. 3. A radio transceiver system comprising radio transceiver means (6a to 6c) for transmitting at least one outbound signal at least at two trans¬ mitting frequencies varying in accordance with a pre¬ determined frequency-hopping sequence and for receiving at least one inbound signal at least at two receiving frequencies varying in accordance with said frequency-hopping sequence, c h a r a c t e r i z e d in that the system comprises a fixed-frequency radio transceiver (6a to 6c) for each pair of transmitting and receiving fre- quencies, and means (5) for switching said at least one out¬ bound signal as a baseband signal from baseband signal processing stages (7a to 7c) to said fixed- frequency transceivers (6a to 6c) and for switching said at least one received inbound signal as a baseband signal from said fixed-frequency trans¬ ceivers (6a to 6c) to the baseband signal processing stages (7a to 7c) in accordance with said frequency- hopping sequence. 4. A system according to claim 1, 2 or 3, c h a r a c t e r i z e d in that said switching means (5) is a switching matrix. 5. A system according to claim 1, 2, 3 or 4, c h a r a c t e r i z e d in that said at least one baseband signal is a serial digital signal. 6. A system according to claim 5, c h a r a c ¬ t e r i z e d in that said serial digital signal is a time-division multiplexed signal comprising eight channel time slots. 7. A system according to claim 6, c h a r a c ¬ t e r i z e d in that the baseband signal processing means are switched to a different radio transmitter or receiver after each transmission or reception of a channel time slot in accordance with said frequency- hopping sequence. 8. A system according to claim 7, c h a r a c ¬ t e r i z e d in that the baseband signal processing means (7a to 7c) are switched to a new transceiver preferably after each transmission or reception of a channel time slot during guard intervals between the channel time slots. 9. A system according to claim 1 or any of ' claims 4 to 8, c h a r a c t e r i z e d in that the radio transmitters are coupled to a common antenna by means of a combiner unit (1) comprising a trans¬ mitting filter for each radio transmitter. 10. A transceiver system according to any of claims 5 to 8, c h a r a c t e r i z e d in that the system comprises several baseband signal processing units (7a to 7c) each processing one received inbound time-division multiplexed signal and one outbound time-division multiplexed signal, and that each baseband unit (7a to 7c) is connectable to said transceivers (6a to 6c) through a serial time- division bus (8, 9) common to the receiving and transmitting direction signals of the baseband unit by said switching means (5). 11. A transceiver system according to claim 10, c h a r a c t e r i z e d in that control signals are transmitted via said serial time-division bus (8, 9) at least from the baseband unit to the trans¬ ceiver.

Inventors: KEMPPAINEN JARI, KEMPPAINEN, JARI
Applicants: TELENOKIA OY
Application year: 1991
Main classification: H04B7
IPC codes: H04B1, H04J13