EFFICIENCY IMPROVING OF THE TIME-FREQUENCY RESOURCES UTILIZATION FOR GSM NETWORKS

M.M. Klymash, T.A. Maksymyuk, M.Ya. Sheremeta, R.Z. Kozlovskiy

Lviv Polytechnic National University

Abstract: 
This article introduces the methods and techniques for improving of the spectral resources utilization effectiveness for GSM mobile network. We suggest the combined use of orthogonal multiplexing and dynamic frequency and channel allocation as an optimal solution for radio access network. Speech quality is an important measurement for the performance evaluation in a wireless mobile communication system since voice is still the most used service. The speech quality evaluation considered in this paper for GSM system employing narrowband and wideband AMR codecs with Orthogonal Sub Channel (OSC) technique. OSC feature proposes the way to double circuit switched capacity for GSM networks. It has introduced two new channel modes, namely Double Full-rate (DFR), and Double Half-rate (DHR), which have doubled capacity in comparison to legacy AMR channel modes. Many of the efforts in standardization are concentrated on studying hardware improvements lead by AMR DHR usage over AMR HR channel mode. Although AMR DFR has not brought hardware efficiency improvements over legacy channel modes, in this paper it is shown that speech quality is improved over AMR HR with the same blocking capacity. Therefore, it is a good solution for some interference-limited networks. Furthermore, we also investigate the speech quality of wideband AMR DFR codecs, which provides a substantial improvement when compared with narrowband AMR. As GSM uses the combination of frequency division multiple access and time division multiple access, the radio channel determines by the frequency slot and the timeslot. When a channel assignment needs to perform because of a newly initiated connection or handover, DFCA will evaluate all the possible channels and then choose the most suitable one in terms of CIR for the assignment. For this reason, an estimate of the CIR is determined for each available radio channel. The pairing of two users in the same radio channel is one of the most critical of all the aspects of radio resource management. The BSC can take advantage of the software-based pairing capability of DFCA to search for the best pair among several candidates. Although the BSC uses part of the DFCA algorithm for pairing, it is not necessary to synchronize BSS, as is usually the case when introducing DFCA. In standard mode, each GSM frequency channel can handle 8 or 16 users when using the FR-and HR-channel mode. Accordingly, the application of OSC to FR and HR calls, the 16 and 32 persons can occupy one frequency channel by double-FR (DFR) and double-HR (DHR), respectively. To maintain QoS parameters, there were introduced the restrictions for a range of using orthogonal subchannel. With use of OSC technique, we propose to distribute the subscribers to three service quality classes. Simulation results confirm the effectiveness of proposed methods, in terms of calls lost probability.