The Research of Data Compression on Abis Interface of GSM Network

Abstract

On the Abis interface which is between BSC(Base Station Controller) and BTS(Base Transceiver Station), the throughput of data is fixed at 2Mbps- As networks become larger and larger, and there are more and more uesrs, signals may be blocked and data may be lost at network when it is busy- And since the half rate technology has been widely used, the bandwidth of the LAPD(Link Access Protocol on the DM Channel) on the Abis interface is becoming limited- As the reason given above, it is very important and useful to increase the throughput of the Abis interface- In order to double the throughput of the Abis interface, the software compression technology is used, which is always used in upper layer of OSI model- This paper proposed a new compression algorithm called LZ77++, taking considering of the latest GSM transport protocol, characteristics of data in the Abis interface- Data in Abis interface is de-muxed and compressed at one side- And the data will be muxed and decompressed at the other side- The proposal described in this paper has been implemented in the A-Bis over IP Gateway system of BroadBand High Technology Inc- The experiemental result has proven that it could increase the throughput of the Abis interface significantly, and it is worthy for further research-

Alternate abstract:

GSM网建网以来,在BSC(Base Station Controller)和BTS(Base Transceiver Station)间的Abis口上，数据传输速率为固定的2Mbps。随着网络规模的发展，特别是用户数的增加，导致了在最忙时会出现控制信道信令严重阻塞及大量的掉话的现象。同时，随着GSM半速率技术的实际应用，Abis中传输的LAPD(Link Access Protocol on the DM Channel)信令带宽日趋紧张。所以，提高Abis接口上传输速率有着非常重要的应用价值。 为了达到GSM系统中Abis接口传输能力倍增的目的，本文尝试采用软件压缩技术将通常在开放系统互连协议中较高层采用的压缩协议应用到物理层上来，以寻求能改善某些特定通信系统传输效能的新型通信设备。 本文参考了现行GSM网络中传输协议，深入分析了Abis信道中传输数据的特点。将现有数据压缩算法中比较成熟的LZ77算法，根据Abis信道数据传输的特点进行改进，提出了数据压缩的一种算法—LZ77++算法。通过借鉴通用数据压缩技术的原理和实现方法，实时地将Abis接口上的数据流进行解复用、压缩，从而扩大传输能力，并在接收端进行解压缩、复用，无损地恢复出原始数据。 该方案已经在宽兆通信高科技有限公司的A-Bis over IP Gateway系统中实现。测试表明这一方法能够较好的压缩Abis接口上的数据，较大的提高Abis接口的带宽利用率，具有较高的进一步研究深化价值。