Maxim Gitlits

Performance between circuit allocation schemes for half- and full-rate connections in GSM

This paper considers three circuit allocation schemes for half- and full-rate connections in the Global system for Mobile Communications (GSM): best fit, repacking, and fair repacking. Analytic numerical methods are used to investigate each schemes blocking probability behavior. The analysis is based on a reduction of the state space to a manageable size. Fair repacking is found to be the fairest and most efficient. However, the best-fit scheme, while being somewhat less efficient and fair, is simpler to implement. The effect on quality of service (QoS) of voice dropouts related to intracell handover (repacking) was found to be negligible.

Adaptive transmission parameters optimisation in wireless multi-access communication

The purpose of this paper is to optimize a wireless link which uses forward error correction (FEC), modulation gain, and for data services, automatic repeat request (ARQ) protocols, with the aim to minimize the bandwidth required. Simulations are used to derive bit error rate values for a range of modulation and FEC code rate parameters. These parameters are optimized to maximize efficiency. We demonstrate that optimal adaptive modulation provides significant efficiency gains. We actually question the use of FEC for a wide (practical) range of signal-to-noise ratios, and demonstrate that in the case of data traffic, optimal adaptive modulation together with ARQ retransmission, in the absence of FEC, provides better efficiency, and/or QoS, than the same system with FEC. Similar results are achieved also for video, where ARQ is not used.

Teletraffic implications of a generic ATM wireless access protocol

This paper examines the performance and efficiency of a generic ATM access protocol, which combines the principles of leaky bucket, max-min fairness and demand assigned multiple access (DAMA), to manage the transmission of ATM cells from wireless terminals/handsets to base stations. The paper proposes a new over the peak ABR service which allows transmission over the agreed ATM peak cell rate (PCR) to better utilize the radio channel. Based on traces of real bursty traffic, we demonstrate by simulation the benefit gained by implementing this new service. By simulation we evaluate the optimal wastage due to queuing and by a simple analytical model the optimal wastage due to errors. We provide the means to support optimal adaptive setting of the code rate and of the signal strength. We demonstrate that even for certain realistic SNR conditions the wastage due to errors can be very high because of retransmission.

FEC Code Rate and Bandwidth Optimisation in WATM Networks

This paper considers data transmission over an error prone Wireless ATM access network. Two inter-related optimisation problems are examined: (1) for a given total allocated channel capacity for a given connection, how to maximise the error prone channel’s throughput, and (2) for a given (bursty) traffic stream with mean rate, how to minimise the required bandwidth. Solutions to these two problems also imply obtaining the optimal Forward Error Correction (FEC) Code Rate. Both optimisation problems consider: (a) the connection traffic stream mean rate, and its level of burstiness; (b) the capacity allocated for FEC redundancy; (c) the size of retransmitted block of data, i.e. Automatic Repeat Request (ARQ) of a frame, packet or a single cell; (d) the capacity allocated for re-transmissions of erroneous blocks of data; and (e) the capacity allocated for guaranteeing tolerable delay to avoid time-outs and congestion collapse. An interesting aspect of the problem is the trade-off between FEC redundancy and the traffic volume of retransmission of erroneous blocks of data. The optimisation is simplified using the maximal power criterion to avoid time-outs and congestion collapse. This maximal power is calculated by simulation using Ethernet traffic traces.

Channel allocation methods for half and full rate connections in GSM

This paper considers five circuit allocation schemes for half and full rate connections in GSM. Analytic numerical methods are used to investigate each schemes blocking probability behaviour. Two members of the repacking family of schemes, repacking with perpetual half slot reservation and repacking with random reservation, are found to be the fairest in terms of blocking probability, and have the highest network utilisation (efficiency). However, the best fit scheme, while being somewhat less efficient and fair, is simpler to implement and does not incur voice dropouts related to intracell handover.

Performance analysis of circuit allocation schemes for half and full rate connections in GSM

GSM uses a TDMA structure with eight slots-per-frame to support speech and data transmission. This paper considers five circuit allocation schemes for half and full rate connections in GSM. Analytic numerical methods are used to investigate each schemes blocking probability behaviour. The analytic solution is based on a reduction of the state space to a manageable size. All three repacking family schemes incur low blocking probability and repacking with perpetual half slot reservation is the fairest scheme.

Dynamic resource allocation with inter-cell interference coordination for 3GPP LTE

In this paper, we propose distributed dynamic resource allocation schemes for future cellular networks to enable efficient utilization of the whole available frequency spectrum. Our algorithms are simple, so that fast resource allocation decisions can be made at the base stations. To enable coordination between base stations, our schemes require inter-base-station signaling of system state information every update interval; we consider different update intervals ranging from milliseconds to seconds. When the load is not too high, our schemes yield gains in average user throughput and the 10% quantile of the user rate distribution compared to an uncoordinated full frequency reuse system. While our schemes are applicable to any OFDMA or TDMA wireless access technology, we focus on their applications to LTE.

Synchronisation and Timing Groups for GSM Networks

GSM networks are optimised for voice services using compact frequency re-use schemes such as 1/1 with fractional loading. GPRS/EDGE codecs require better quality channels to support higher data throughput, i.e. channels with lower collision rates and better average carrier-to-interference ratio (CII). With the continuing growth of mobile data traffic, networks must improve channel quality in a compact re-use environment. To achieve this, we recommend the introduction of timing synchronisation for base stations (BS) in a GSM/GPRS/EDGE network. Our analysis shows that BS synchronisation leads to a reduction in collision rates that can be exploited for either C/I or capacity improvement. More importantly, we propose timing groups (TG) for a synchronized network. In conjunction with frequency planning, TG offers greater flexibility in network design by providing superior quality channels to a category of users without dividing the available spectrum into carrier groups with different re-use schemes

WATM operation optimisation based on effect of FEC code rate and ARQ retransmission

This paper applies a new methodology to different coding schemes for WATM efficiency evaluation. This methodology is based on the separation of error based efficiency (EBE), which is the ratio between the mean raw data rate and the raw data rate plus all overheads associated with error corrections and retransmission of erroneous blocks of data, from queuing based efficiency (QBE), which is the ratio between the error free data rate and the overall channel capacity. We compare between the efficiency of convolutional coding (in the case of binary transmission and high level modulation transmission) and turbo coding. We show that under most value of signal to noise ratio (SNR), turbo coding is the most efficient. We also provide means to support optimal adaptive setting of the code rate and demonstrate the improvement gained by implementing adaptive forward error correction code rate. We further demonstrate that, for certain realistic SNR conditions, the wastage due to retransmissions can be very high.

Wireless Link Dimensioning and Transmission Parameters Optimisation

This paper provides guidelines for Wireless ATM (WATM) link dimensioning and coding parameters optimisation subject to meeting specified Quality of Service (QoS) requirements. It takes into consideration a comprehensive set of coding as well as teletraffic issues: (1) effects of retransmissions of erroneous packets using Automatic Repeat Request (ARQ) protocols, (2) modulation efficiency (3) Forward Error Correction (FEC) redundancies, and (4) effect of traffic burstiness on loss and delay. Simulations are used to derive Bit Error Rate values for a range of modulation efficiency and FEC Code Rate parameters. These parameters are then optimized to obtain maximal efficiency. We discover that adaptive modulation, where modulation efficiency is dynamically optimized, provides significant efficiency gains. In fact, we demonstrate that in many practical situations, optimal adaptive modulation together with or even without ARQ retransmission in the absence of FEC provides better efficiency and/or QoS than the same system with FEC.