RADIO PAGING SYSTEM WITH DIFFERENT TRANSMISSION SPEEDS AND RECEIVER THEREFOR

Abstract: A transmitter for a paging system, includes degree indicating means (11) for producing a first signal which is representative of a degree N in response to a signal which is representative of a bit rate N.R (16), where N is a positive integer and R is a basic bit rate, interleaving means (12) for N-degree interleaving input data having the bit rate N.R in response to the first signal to produce an interleaved signal and transmitting means (13, 14) for transmitting the inter­ leaved signal.

Description: BACKGROUND OF THE INVENTION The present invention relates to a radio paging system and, more particularly, to a paging system which offers a service at several different bit rates and a receiver for the same. The current trend in paging systems is towards a higher bit rate which would enable an increase in traffic as well as the effective use of frequency. A method heretofore proposed for increasing the bit rate of a paging signal consists in simply multiplying clock frequency by N to make the bit rate N-fold. This kind of method, however, has some problems as enumerated below. (1) Receivers of different bit rates cannot coexist in a single paging system; and (2) while each codeword usually undergoes error correcting coding, an increase in bit rate results in a decrease in the time length of one codeword and, therefore, the signal becomes susceptible to burst errors which frequently occurs on radio channels due to fading. Another prior art implementation for higher bit rates is changing the bit rate depending upon the kind of information (e.g. 300 bits per second for an address and 600 bits per second for a message), as disclosed in, for example, U.S. Patent 4,642,632 which is assigned to the applicant of the instant application and issued February 10, 1987 to Ohyagi et al. Such an implementation, however, is incapable of changing the bit rate depending upon the traffic because the bit rate for one kind of information is fixed (e.g. 300 bits per second for an address without exception). A feature of an embodiment to be described is the provision of a radio paging system which accommodates receivers of different bit rates, and is resistive to burst errors even if the bit rate is increased. In a particular embodiment to be described a transmitter for a paging system includes degree indicating means for producing a first signal representative of a degree N in response to a signal which is representative of a bit rate N·R, where N is a positive integer and R is a basic bit rate, interleaving means for N-degree interleaving input data having the bit rate N·R in response to the first signal to produce an interleaved signal, and transmitting means for transmitting the interleaved signal. A paging receiver to be described includes receiving means for receiving a signal whose bit rate is N·R where N is a positive integer and R is a basic bit rate; bit rate indicating means for outputting a first signal which is representative of the N; de-interleaving means for N-degree de-interleaving the received signal in response to the first signal to produce a de-interleaved signal; and deciding means for deciding whether or not a paging address number included in the de-interleaved signal is an address number which is assigned to the receiver. Specifically, the interleave and de-interleave degree is varied in proportion to the bit rate, i.e., the second-degree de-interleave is performed when the bit rate is 2R (N = 2), third-degree de-interleave is performed when the bit rate is 3R (N = 3), and N-degree de-interleave is performed when the bit rate is N·R. Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a schematic block diagram showing a transmitting side of a radio paging system embodying the present invention; Fig. 2 is a block diagram showing a specific construction of an interleave circuit which is included in the system of Fig. 1; Figs. 3A to 3D are views each showing a sequence for designating addresses of a random access memory (RAM) as shown in Fig. 2; Fig. 4 is a timing chart demonstrating the operation of the interleave circuit of Fig. 2; Fig. 5 is a schematic block diagram showing a receiver of the radio paging system in accordance with the present invention; Fig. 6 is a timing chart representative of the operation of the circuit shown in Fig. 5; Fig. 7 is a block diagram showing a specific construction of a de-interleave circuit which is built in the receiver of Fig. 5; and Fig. 8 is a timing chart representative of the operation of the de-interleave circuit shown in Fig. 7. DETAILED DESCRIPTION OF THE EMBODIMENTS Referring to Fig. 1, a transmitting side of a radio paging system in accordance with the present invention is shown and includes an interleave-degree indicating table 11. A signal S B for designating a particular bit rate of transmit data is applied through a terminal 16 to the interleave-degree indicating table 11 which then produces a signal S D for indicating an interleave degree proportional to the designated bit rate. For example, when the designated bit rate is N·R (N = 1, 2, 4, 8, ...), the table 11 produces an interleave degree indicating signal S D of N. Here, R is representative of a basic bit rate which is to be used while interleave is not performed. The output S D of the table 11 is fed to an interleave circuit 12. Also fed to the interleave circuit 12 area clock (c) and a reset (r) pulse which are generated by a clock generator 17. In response, the interleave circuit 12 applies N-degree interleave to input data d₁ which come in through a terminal 15, the resulting signal d₂ being delivered to a modulator and transmitter section 13. This section 13 modulates a carrier wave with the signal d₂ by, for example, the frequency shift keying (FSK) principle and, then, transmits it through an antenna 14. The signal S B indicating the bit rate N·R may be serial data which is fed from a telephone exchange. In such a case, the interleave-degree indicating table 11 may be implemented with a serial-to-parallel (S/P) converter for converting the serial data into parallel data, and a read-only memory (ROM) for producing a signal S D indicating the interleave degree data N addressed by the parallel data. Referring to Fig. 2, the interleave circuit 12 is shown in detail. As shown, the interleave circuit 12 includes a random access memory (RAM) 21, N-bit counters 23 and 24, L-bit counters 22 and 25, a T flip-flop (F/F) 26, an inverter 27, clock generators 28 and 29, and a delay circuit 30. Here, L is representative of the length of a codeword to be interleaved. The input data d₁ applied to an input terminal 31 are sequentially written in those memory areas of the RAM 21 which are specified by addresses which are in turn designated by the L-bit counter 22 and N-bit counter 23. The output data d₂ are sequentially read out of those areas of the RAM 21 which are designated by the addresses which are in turn designated by the L-bit counter 25 and N-bit counter 24, the data d₂ being applied to an output terminal 32. The RAM 21 is divided into two discrete banks one of which is used for read-out while the other is used for write-in. Specifically, a write bank and a read bank are alternately selected on an interleave block basis by the T F/F 26 and inverter 27. The clock generators 28 and 29 generate, respectively, clocks c1 and c2 (= N₁·R and N₂·R) which are proportional to the interleave degrees N₁ and N₂, respectively. The delay circuit 30 serves to delay the input S D1 indicating N₁ by one interleave block, producing a signal S D2 indicating the interleave degree N₂ of output data d₂. The operation of the circuit shown in Fig. 2 will be described with reference to Figs. 3A to 3D and 4. In the figures, L is representative of the codeword length of a paging signal, and one interleave block length is assumed to be N x L. Further, (a₁₁, a₁₂, ..., a 1L ), (a₂₁, a₂₂, ...., a 2L ), (b₂₁, b₂₂, ..., b 2L ) each are a codeword of a paging signal. As shown in Fig. 4, assuming that the transmit data d₁ are different in bit rate from one interleave block to another, each interleave block having a fixed length. The interleave degree is proportional to the bit rate. While the interleave degree N₁ is adapted for writing data d₁ in the RAM 21, the interleave degree N₂ is an interleave degree which occurs one block after the interleave degree N₁ and is adapted for reading data d₂ out of the RAM 21. Clocks c1 and c2 have, respectively, frequencies N₁.R and N₂.R which are proportional to the interleave frequencies N₁ and N₂ respectively. A reset signal τ is applied to a terminal 33, Fig. 2, at the head of an interleave block as occasion demands, in order to match in phase the write-in counters 22 and 23 and the read-out counters 24 and 25. The input data d₁ are written in those memory areas of the RAM 21 which are designated by the addresses as specified by the L-bit and N-bit counters 22 and 23 respectively, in either one of the sequences shown in Figs. 3A and 3C. Specifically, Fig. 3A shows a write-in order for the interleave degree of 1; the input data are written in the sequence of a₁₁, a₁₂, ..., a 1L . Fig. 3C shows a write-in order for the interleave degree of 2; the input data are written in the sequence of a₂₁, a₂₂, ..., a 2L and, then, b₂₁, b₂₂ , ..., b 2L . On the other hand, the output data d₂ are read out of those memory areas of the RAM 21 which are designated by the addresses as specified by the N-bit and L-bit counters 24 and 25, respectively, in the order shown in Fig. 3B or 3D. Specifically, Fig. 3B shows a read-out order corresponding to the interleave degree of l; the data are read out in the same sequence as they are written in. Fig. 3D shows a read-out order corresponding to the interleave degree of 2; the data are read out in the sequence of a₂₁, b₂₁, a₂₂, b₂₂, ..., a 2L , b 2L . As a result, as shown at the bottom of Fig. 4, the transmit data d₂ are produced interleaved at the interleave degree which is proportional to the bit rate. Referring to Fig. 5, a receiver of the paging system in accordance with the present invention is shown. As shown, the receiver includes an antenna 101 and a receiver and demodulator section 102 which receives and demodulates a modulated carrier wave coming in through the antenna 101 to produce a demodulated signal d₃. The carrier wave may be FSK modulated. A de-interleave circuit, or N-degree de-interleave means 103, N-degree de-interleaves the demodulated signal d₃ in accordance with a bit rate (N·R) which is specified by a bit-rate indicating table, or bit-rate indicating means, 104. It is to be noted that data indicating the degree N are stored in the table 104 beforehand. A paging signal detector section 105 energizes a speaker or like annunciating means 106 when it has detected a paging signal from the receiver as a de-interleaved output d₄ of the de-interleave circuit 103. Further, a clock sync section 107 functions to produce a clock c and a reset pulse τ which are synchronous to the demodulated signal d₃, at the bit rate specified by the bit-rate indicating table 104. In Fig. 6, d₃ and d₄ are representative of, respectively, the demodulated signal d₃ and the deinterleaved signal d₄ as shown in Fig. 5, N being assumed to be 1, 2 and 4. The codeword length of a paging signal is assumed to be L and the interleave block length, N x L. Also, (a₁₁, a₁₂, ..., a 1L ), (a₂₁, a₂₂, ..., a 2L ) and so on each represents a codeword of a paging signal. Referring to Fig. 7, a specific construction of the bit rate designating means 104 and N-degree de-interleave means 103 of Fig. 5 is shown in a block diagram. In the figure, there is shown a RAM 201 having a data input terminal D IN , a data output terminal D OUT , an input address input terminal A IN , and an output address input terminal A OUT . Assuming that the codeword length of the paging signal is L, the interleave degree is N, and the interleave block length is N x L, there are provided L-bit counters 203 and 206, N-bit counters 202 and 207, and a T F/F 204. In the various sections shown in Fig. 7, C,RE, N and OVR stand for, respectively, a clock input terminal, a reset input terminal, a frequency division number (N) input terminal, and an overflow output terminal. The reference numeral 205 designates an inverter. The circuit elements 201 to 207 described so far constitute the N-degree de-interleaving means. A ROM 208 which corresponds to the bit rate indicating table 104 of Fig. 5 is adapted to designate a bit rate (N·R) and produces a signal S D indicating a value N. Here, the basic bit rate R is assumed to be determined beforehand. The input address (A IN ) of the RAM 201 is designated by the N-bit counter 202, L-bit counter 203 and T F/F 204. Assuming that the output signals of the counters 202 and 203 and T F/F 204 are respectively a₁, a₂ and a₃ (a₁ = 0 to (N-1), a₂ = 0 to (L-1), a₃ = 0 or 1), the input address (A IN ), is expressed as: A IN = a₃·L·N + a₂·N + a₁ Likewise, the output address (A OUT ) is designated by the L-bit counter 206, N-bit counter 207 and inverter 205. Assuming that the output signals of the L-bit counter 206, N-bit counter 207 and inverter 205 are, respectively, a'₁, a'₂ and a'₃ (a'₁ = 0 to (L-1), a'₂ = 0 to (N-1), a'₃ = 0 or 1), the output address (A OUT ) is given by: A OUT = a'₃·L·N + a'₂·L + a'₁ where a'₃ is an inverted version of a₃, i.e., when a₃ is 0, a'3 is 1 while, when a₃ is 1, a'₃ is 0. Hence, the data applied to the RAM 201 are N-degree deinterleaved and, then, outputted by the RAM 201. Specifically, when N is 2, the data which are inputted in the sequence of a₁₁, b₁₁, a₁₂, b₁₂, a₁₃, b₁₃, ..., a 1L , b 1L , ... are outputted in the sequence of a₁₁, a₁₂, a₁₃, ..., a 1L , b₁₁, b₁₂, b₁₃, ..., b 1L , ..., as shown in Fig. 8. It is to be noted that one block of delay occurs because RAM 201 has two discrete banks. Contrary to the interleaving circuit (Fig. 2), however, no delay circuit is required because a bit rate of N·R is fixed for the receiver. In summary, it will be seen from the particular embodiments described that one paging system can accommodate receivers of different bit rates since de-interleave of a degree which is proportional to a bit rate (N·R) is performed, allowing a transmitting bit rate which matches with a message or traffic to be selected. Further, because the codeword length (time length) of a paging signal remains constant within the range of time lag of 1/R with no regard to the bit rate, burst errors of substantially the same length, which frequently occur on a radio channel due to fading, can be corrected by the same error correcting code with no regard to the bit rate. This solves the problem particular to the prior art system that an increase in bit rate aggravates the susceptibility to burst errors. It will be understood that, although the invention has been described, by way of example, with reference to particular embodiments, variations and modifications thereof, as well as other embodiments may be made within the scope of the appended claims. For example, a receiver for a paging system may include receiving means for receiving a signal whose bit rate is N·R where N is a positive integer and R is a basic bit rate; bit rate indicating means for outputting a first signal which is representative of the N; de-interleaving means for N-degree de-interleaving the received signal in response to said first signal to produce a de-interleaved signal; and deciding means for deciding whether or not a paging address number included in said de-interleaved signal is an address number which is assigned to said receiver.

Claims: A transmitter for a paging system, including degree indicating means (11) for producing a first signal representative of a degree N of interleaving in response to a signal which is representative of a bit rate N·R, where N is a positive integer and R is a basic bit rate, interleaving means (12) for N-degree interleaving input data having the bit rate N·R in response to the first signal to produce an interleaved signal, and transmitting means (13) for transmitting the interleaved signal. A transmitter in accordance with claim 1, wherein the transmitting means (13) includes means for frequency shift keying (FSK) modulating a carrier wave with the interleaved signal. A transmitter in accordance with claim 1, wherein the interleaving means includes memory means (21) having a first and a second memory bank, means (26, 27) for switching the first and second memory banks to a write-in and a read-out mode alternately, for each interleave block of the input data, first address outputting means (28, 22, 23) for outputting a first address in response to the first signal, delaying means (30) for delaying the first signal by one interleave block of the input data, second address outputting means (29, 24, 25) for outputting a second address, which is produced by N-degree interleaving of the first address, in response to an output of the delaying means, means for writing the input data in a memory area of any one of the first and second memory banks which corresponds to the first address, and means for reading the interleaved signal out of a memory area of any one of the first and second memory banks which corresponds to the second address. A transmitter in accordance with claim 3, wherein the memory means includes a random access memory (21). A transmitter in accordance with claim 3, wherein the interleave block has a length of N x L where L is a length which constitutes one frame of the input data at the basic bit rate, each of the first and second address outputting means including an N-bit counter (24) and an L-bit counter (25). A receiver for a paging system, including receiving means (102) for receiving a signal containing input data whose bit rate is N·R where N is a positive integer representative of the degree of interleaving and R is a basic bit rate, bit rate indicating means (104) for outputting a first signal representative of the degree N of interleaving, the first signal being stored in advance, de-interleaving means (103) for N-degree de-interleaving the received signal in response to the first signal to produce a de-interleaved signal, and deciding means (105) for deciding whether or not a paging address number included in the de-interleaved signal is an address number which is assigned to the receiver. A receiver in accordance with claim 6, further including alarm means (106) for producing an audible alarm in response to an output of the deciding means (105). A receiver in accordance with claim 6, wherein the de-interleaving means (103) includes memory means (201) having a first and a second memory bank, means (204, 205) for switching the first and second memory banks to a write-in and a read-out mode alternately, for each interleave block of the input data, first address outputting means for outputting a first address in response to the first signal, second address outputting means (206, 207) for outputting a second address, which is produced by applying N-degree de-interleave to the first address, in response to the first signal, means for writing the received data in a memory area of any one of the first and second memory banks which corresponds to the first address, and means for reading the de-interleaved signal out of a memory area of any one of the first and second memory banks which corresponds to the second address. A receiver in accordance with claim 8, wherein the memory means includes a random access memory (201). A receiver in accordance with claim 8, wherein the interleave block has a length of N x L where L is a length which constitutes one frame of the input data at the basic bit rate, each of the first and second address outputting means including an N-bit counter (207) and an L-bit counter (206). A paging system including means (12, 13) responsive to a first signal for N-degree interleaving a paging signal having a bit rate of N·R where N is a positive integer representative of the degree of interleaving, and R is a basic bit rate and transmitting the N-degree interleaved paging signal, degree indicating means (11) for producing the first signal representative of the degree N of interleaving in response to a signal which is representative of the bit rate N·R, means (103) responsive to a second signal for N-degree de-interleaving signal, bit-rate indicating means (104) for outputting the second signal representative of the degree N of de-interleaving, the second signal being stored in advance, and deciding means (105) for deciding whether or not the de-interleaved signal includes a desired paging signal. A system in accordance with claim 11, further including means (106) for producing an audible alarm in response to an output of the deciding means (105) which shows that the de-interleaved signal includes the desired paging signal. A method of transmitting and receiving a paging signal, including the steps of N-degree interleaving, in response to a first signal, a paging signal, whose bit rate is N·R where N is a positive integer, representative of the degree of interleaving of the paging signal, and R is a basic bit rate, outputting the first signal representative of the degree N of interleaving in response to a signal which is representative of the bit rate N·R, transmitting the interleaved paging signal, N-degree de-interleaving, in response to a second signal, the transmitted paging signal to produce a de-interleaved signal, storing, in advance, the second signal representative of the N-degree of de-interleaving, and outputting the stored second signal to the N-degree deinterleaving step, and deciding whether or not the de-interleaved signal includes a desired paging signal. A method in accordance with claim 13, further including the step of generating an audible alarm when it is decided that the de-interleaved signal includes the desired paging signal. A method of receiving a paging signal, including the steps of receiving a signal whose bit rate is N·R where N is a positive integer representative of the degree N of interleaving, and R is a basic bit rate, storing, in advance, a first signal representative of a degree N of de-interleaving, N-degree de-interleaving the received signal in response to the stored first signal to produce a de-interleaved signal, and deciding whether or not the de-interleaved signal includes a desired paging signal. A method in accordance with claim 15, further including the step of producing an audible alarm when the de-interleaved signal includes the desired paging signal.

Inventors: OYAGI, TAKASHI C/O NEC CORPORATION, SATO, TOSHIFUMI C/O NEC CORPORATION
Applicants: NEC CORPORATION
Application year: 1987
Main classification: H04Q7
IPC codes: H04L1, H04L29, H04W88, H04W8