KR100241328B1 - Method of sequence assignment to base station in a cdma wll system - Google Patents

Abstract

A wireless local loop (WLL) system is a system that replaces a wired network between a conventional telephone station and a subscriber station by wireless, and various methods and systems have been proposed. The present invention proposes a method of operating a base station in a WLL system using a CDMA method and a method of allocating a sequence to each base station to distinguish each base station. In the WLL system, since there is little or very limited mobility of a terminal station, there is no need to perform handoff between base stations, and thus synchronization between base stations is unnecessary. The present invention proposes an asynchronous system between base stations and, unlike the conventional CDMA scheme, proposed a base station sequence allocation scheme capable of independent sequence operation for each base station.

Description

Base station sequence allocation method in code division multiple access wireless subscriber network system

The present invention relates to a method for allocating sequences to distinguish each base station in a wireless local loop (WLL) system using a CDMA scheme.

The mobile communication system using the CDMA method of the prior art has been proposed various types of systems from various companies in each country. In the US-based Qualcomm system of IS-95 standard system, a GPS receiver is used to maintain synchronization between base stations. In addition, the base station uses a pseudo noise code called a long code of 2 ⁴² -1 cycles to directly spread the data symbols, and a short code of 2 ¹⁵ -1 cycles for distinguishing the base stations. Pseudo noise code is used.

Here, the short code is generated P _i (x) = x ¹⁵ + x ¹³ + x ⁹ + x ⁸ + x ⁷ + x ⁵ + 1 and P _Q (x) = x ¹⁵ + x ¹² + x ¹¹ + x ¹⁰ Generated by + x ⁶ + x ⁵ + x ⁴ + x ³ + 1 and multiplied by the data of in-phase and quadrature components, respectively. At this time, the sequence generated by the expression P _I (x) and P _Q (x) is called a pilot PN sequence.

1 shows a base station transmitter of an existing CDMA cellular system using a long code and a short code. Referring to FIG. 1, the generated traffic information 101 is processed according to the modulation process in the traffic information processing unit 102 so that the long code generated by the long code generation and processing unit 103 and the exclusive logical sum of the multiplier 104 are output. Multiply by the (exclusive-OR) function. In addition, the Walsh code generated by the Walsh code generator and the multiplier 106 are exclusively ORed for orthogonal modulation. Then, the traffic data is divided into I and Q paths so that the short code generator 107 for the I channel. And multiplied by the respective multipliers 109 and 110 by the PN sequence generated in the short code generator 108 for the Q channel and then processed by the baseband signal processing and the IF modulators 111 and 112. Finally, it is added by the adder 113 and then output to the RF unit.

Meanwhile, the base station code assignment scheme in the conventional scheme using the system having the structure shown in FIG. 1 is as follows. Each base station uses the time offset of the pilot PN sequence to distinguish the forward CDMA channel of each base station, and the time offset may be reused in the CDMA cellular system. Different pilot channels, ie, forward channels, are distinguished by offset indices from 0 to 511, which represent the degree of deviation from the zero offset pilot PN sequence. The zero offset pilot PN sequence is the output of the sequence starting at the beginning of every two seconds in time relative to the base station transmission time. For both I and Q sequences, the start of the zero offset pilot PN sequence is the sequence state after 15 zeroes have passed. After 14 consecutive zeroes, the 15th zero is forcibly inserted. The detailed operation method is shown in FIG. 2. ²¹⁵ overall to be used for base station differentiator that is, 32768 (301) taking into account a single offset in chips of 64 chip units first base station 302 from the 512-th base station 305, to allow to distinguish the base station do. That is, for a given pilot PN sequence, the offset is equal to 64 times the index value. At any two second boundary time point, the first base station 302 uses the first chip 306 to the 64th chip 307, and the second base station 303 uses the 65th chip 308 to 128th chip 309. Use The same rule applies to the third base station 304 and subsequent base stations.

Over time, each base station uses up one cycle of 32768 chips, but the offset of 64 chips between each base station is always maintained. Figure 4 shows this.

Figure 3 shows the shift register state when as many as two chips have elapsed at any two second boundary. Base station 1 401 uses the third chip 404 to the 66th chip 405, and base station 2 402 uses the 67th chip 406 to 130th chip 407, and 512. The first base station 403 passes back through the 32707 th chip 408 to the 32768 th chip 409 and uses the second chip 410.

According to the above, in the prior art, since the base stations use the entire period of the common PN sequence while the base stations are offset from each other in order to distinguish the base stations, not only the sequence operation for each base station can be performed independently but also the base station using the GPS receiver. The time offset between them must be strictly observed.

This prior art approach is inadequate and wasteful in WLL systems with limited mobility, which complicates the system and increases the cost of the system.

The object of the present invention for solving the above problems, unlike the conventional CDMA system, by operating the timing between the base stations asynchronously without using an expensive GPS receiver, pseudo noise code without distinguishing between long code and short code By using only one code, base station identification and spread spectrum can be simplified and system cost can be greatly reduced, thus enabling a competitive CDMA wireless communication system both internally and externally.

1 is a block diagram of a traffic information transmitter of a base station in a CDMA cellular system according to the prior art.

2 is a diagram illustrating a sequence usage form of each base station at a 2-second boundary according to the prior art.

3 is a diagram illustrating a sequence usage form of each base station when two chips have elapsed at a two second boundary according to the prior art.

4 is a block diagram of a traffic information transmitter of a CDMA WLL system base station according to the present invention;

5 is a diagram illustrating a method of using a base station sequence according to the present invention.

6 is a flow chart for base station sequence allocation of the present invention.

〈Description of the symbols for the main parts of the drawings〉

202: traffic information processing unit 203: Hadamard code generation unit

204, 205, 208, 209: multipliers 206, 207: PN sequence generator

210, 211: baseband signal processing and IF modulator

212: summer

The base station sequence allocation method of the present invention for achieving the above object, after determining the number of base stations, the PN sequence length to be used per base station and the PN sequence length to be used in the entire system according to the network operation and cell arrangement plan A first step of generating a PN sequence; When the PN sequence is generated, a second process of allocating a unique PN sequence interval used for each base station by a predetermined time unit is repeated by repeating the set number of base stations to operate the base stations asynchronously with each other. It is characterized in that the spread and the base station can be distinguished.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

4 shows a traffic information transmitter of a CDMA system base station according to the present invention. The traffic information 201 is divided into I and Q data through the traffic information processing unit 202, and includes one code generated from the Hadamard code generation unit 203, which is an orthogonal code, and the I and Q paths. Each of the multipliers 204 and 205 is exclusive OR. The I and Q information data multiplied with the Hadamard code are the exclusive ORs of the PN sequences generated by the PN sequence generators 206 and 207 for the I and Q channels and the multipliers 208 and 209 in the I and Q paths, respectively. The baseband signal is processed by the baseband signal processing and IF modulators 210 and 211, and then added by the adder 212 and transmitted to the RF unit.

FIG. 5 shows a usage form of a base station sequence used in the system proposed in FIG. In FIG. 5, as an example, it is assumed that the total number of PN sequences used for base station classification is 2 ³² -1 = 4,294,967,295 (510). Since the number of PN chips allocated to the base station varies according to the clock rate and bandwidth used, the proposed scheme makes the total number of PN chips used by one base station corresponding to 20 msec units regardless of the specific number of PN chips. If the number of PN chips used by the base station 1 501 is k from the first chip 502 to the kth chip 503, the number of PN chips used by the base station 2 504 is from the k + 1th chip 505. There are k up to the 2kth chip 506. The same principle applies to the base station 3 (507).

6 is a flowchart for base station allocation of PN seeds.

PN seed refers to an initial state value of a code generator for generating a PN code. Once the initial value is given, the PN code generator will automatically generate the next state value. The first step in the flowchart is the beginning of this algorithm 601. Next, the step 602 of determining the number (K) and the code length of the base station according to the network operation and cell deployment plan. The code length determines both the code length to be used per base station and the code length to be used in the entire system. The code length to be used in the whole system should be large enough to accommodate the total number of base stations to be served. When the above variables are determined, an initial state value of the PN code generator is determined 603 to drive the generator 604. When the PN code is generated, a timer of m seconds from the desired time is driven (605). In this case, m seconds is a time corresponding to the total length of the PN code allocated to one base station. When the timer is off (606), the code generator is stopped (607) and n bits are selected from the code generator (608). The n bits correspond to the seed to be used by one base station. The selected seed is assigned to any one base station k (609), and then selects an unassigned base station (610). The seed is allocated as many as the number of base stations K designed in this manner (611) and the algorithm is finished (612). If there are still more base stations to which seed is to be allocated, the process proceeds to step 604 of driving the PN code generator again, in which a newly generated PN code section and a PN code section already allocated to the base station do not overlap.

As described above, in the CDMA communication system, each base station is operated asynchronously, and thus, unlike the conventional method, a GPS receiver is not required, and the system hardware portion can be reduced by performing data spreading and base station classification by one code. The system configuration and operation can be simplified at the same time compared to the conventional method.

As a result, the production and operating costs of the system can be greatly reduced, allowing for the production of more competitive products.

Claims (4)

A first step of generating a PN sequence after determining a number of base stations, a pseudo noise (PN) sequence length to be used per base station, and a PN sequence length to be used in the entire system according to a network operation and a cell layout plan; When the PN sequence is generated, a second process of allocating a unique PN sequence interval used for each base station by a predetermined time unit is repeated by repeating the set number of base stations, thereby operating base stations asynchronously. A base station sequence allocation method in a CDMA type WLL system, characterized by being able to spread data and distinguish a base station by using a single PN sequence. The method of claim 1, The unique PN sequence interval is a base station sequence allocation method in the WLL system of the CDMA system, characterized in that for assigning the initial state value of the PN code generator consisting of n bits to any one base station. The method of claim 1, The time base station sequence allocation method in a CDMA type WLL system, characterized in that the time corresponding to the total length of the PN code allocated to one base station. The method of claim 1, The base station sequence allocation method in a CDMA WLL system, characterized in that the PN sequence length to be used in the entire system is determined to accommodate all the number of the base station.

Images