EGPRS Research Articles

Power Control for Packet Voice Service with Application to EDGE Wireless System

Using the enhanced data rates for GSM evolution (EDGE) system with cyclic frequency hopping as an example, we apply a Kalman-filter power control method based on interference tracking to packet voice service in wireless networks. Our results show that the power-control method significantly improves the spectral efficiency by enabling the 1/3 frequency reuse while maintaining a stringent requirement of 2% packet loss probability for voice service. Specifically, for allocated spectrum of 1.8, 3.6 and 5.4 MHz, the 1/3 reuse with the Kalman power control can yield 102.5%, 49.5% and 32.5% improvement in spectral efficiency, respectively, over the 3/9 reuse (regardless of whether or not power control is used). We also compare the performance of the Kalman method with a traditional signalto-interference-ratio method and a control method that is based on the last interference measurement. We find that appropriate selection of power for the first packet of each talk spurt and the filtering function for noisy measurements are crucial in providing high system capacity for packet voice service. For the EDGE system, we also identify a need for shortening the power update period, which is 480 ms in the specifications.

Performance evaluation of suboptimal decoding schemes for tail biting convolutional codes in EDGE headers

The performance of several suboptimal decoding schemes for a tail biting convolutional code used in enhanced data rates for global evolution (EDGE) headers, compared with an optimal decoding scheme, is evaluated. An interference-limited cellular radio environment is considered. The impact of mobile speed is also assessed.

MIMO MAP equalization and turbo decoding in interleaved space-time coded systems

Decoding of space-time codes in frequency-selective fading channels is considered. The approach is based on iterative soft-in soft-out equalization and decoding. It is applicable to space-time coded systems that deploy symbol/bit interleavers. We focus on the equalization stage by extending the Ungerboeck equalizer formulation to a multiple-input multiple-output time-variant channel. The resulting structure comprises a bank of matched filters, followed by an a posteriori probabilities calculator that runs the Bahl-Cocke-Jelinek-Raviv/maximum a posteriori algorithm with an appropriate metric. Simulation results are reported for space-time bit-interleaved codes designed over the enhanced data rates for GSM evolution (EDGE) air interface.

Iterative data detection and channel estimation for advanced TDMA systems

This letter presents a new receiver for Q-ary transmission, where all receiver blocks are embedded in an iterative structure. Packet data transmission in Global Systems for Mobile communications (GSM) and Enhanced Data rates for Global Evolution (EDGE) are considered as examples. A low-complexity soft-in-soft-out detector for EDGE is introduced and its modification suitable for iterative detection is derived. Application of iterative detection and channel estimation techniques in GSM/EDGE shows a significant performance enhancement. Additional improvement may be obtained if the iterative processing is applied to packet retransmission schemes.

Iterative receiver concept for TDMA packet data systems

In this paper we present an iterative receiver concept that improves the radio link performance of TDMA mobile communication systems. We consider sub-optimal receiver structures comprising of channel estimator, detector and channel decoder, where the performance is improved by iterative data processing among the receiver blocks. As a practical example, we consider packet data transmission in GSM and Enhanced Data rates for Global Evolution (EDGE). Low-complexity soft-in-soft-out (SISO) equalizers for EDGE are introduced and its modifications suitable for iterative detection in EDGE are derived. Application of iterative detection and channel estimation techniques in GSM/EDGE shows a significant performance improvement. Furthermore, we show that retransmission schemes specified for EDGE also benefit from iterative data processing. Copyright © 2003 AEI.

Performance of a shared packet wireless network with interactive data users

This paper studies the user-perceived performance of a shared packet wireless network for interactive data applications such as Web-browsing. We have defined a new measure: the Equivalent Circuit Rate (ECR) for a user in a shared access network is the dedicated access circuit rate that would be required by the user in order to have an equivalent user experience. The ECR measure is intuitive, useful and robust. We present a simple analytical model based on a closed queueing network with a finite population of interactive data users whose traffic can be modeled as ON/OFF traffic with feedback. The analytical results are consistent with our detailed simulations, where we study TCP-based Web traffic simulations for an EDGE (Enhanced Data Rates for GSM Evolution) TDMA system using realistic workload models. Our study incorporates constant bit-rate channels, variable bit-rate channels, as well as mixed user groups with different channel conditions. We show that a shared wireless network is well characterized by simple parameters that depend only on mean statistics, for a broad range of scenarios. ECR is well approximated by R × (1 - U), where U is the utilization and R is the effective shared channel rate; this result holds even if different user groups have different rates or the channel rates are variable. These results will be useful in network dimensioning, admission control, and for defining quality of service targets for different user groups.

Statistical Estimation of Fast Varying Channels for Cellular Mobile Telecommunications Systems

The time variant environment in fast channels severely impacts on the performances of classical equalization techniques. A method is proposed here to circumvent this problem, particularly in the severe channel with fast behaviour. To improve the Bit Error Rate (BER) at the receiver, a new approach is proposed for the channel impulse response (CIR) estimation in the Enhanced Data rates for GSM Evolution (EDGE) cellular system. The computation of the CIR h(t) (finite impulse response filter) is performed by using the Least Squares algorithm. Then, a statistical estimation of the CIR is achieved to update the coefficients of the equalizer filter. Computer simulation results show that statistical estimation (CIR re-estimation) provides significant improvement with 250 km/h vehicle speed (RA250): the bit error rate (BER) is 20% lowered for data bits far from the middle of the burst.

Overview and comparison of equalization schemes for space-time-coded signals with application to EDGE

This paper describes and compares several practical equalization schemes for space-time-coded transmissions over broadband wireless channels. For space-time trellis codes (STTCs), we describe and compare two reduced-complexity trellis-based joint equalization and decoding schemes whose performance is further optimized by a front-end finite-impulse response (FIR) channel-shortening prefilter. For space-time block codes, we describe and compare three joint equalization and decoding schemes based on a block-level implementation of the well-known Alamouti scheme either in the time or frequency domains. We consider the third-generation time division multiple access (TDMA) cellular system known as Enhanced Data rates for Global Evolution (EDGE) and recommend a promising equalization scheme for space-time trellis-coded and for Alamouti-type space-time block-coded dual-antenna transmissions based on simulation results for typical urban channel conditions where the delay spread is few symbol periods.

Joint optimization of FIR prefilter and channel estimate for sequence estimation

We provide simple analytical results for the coefficients of a finite-impulse response (FIR) prefilter and the effective channel impulse response (IR) for use in cellular communication systems. We show that using a FIR filter with both causal and anticausal filter taps, it is possible to find the jointly optimized impulse response, such that the signal-to-noise ratio is maximized in the least-squares sense. We show via computer simulation for 8-ary phase-shift keying in Enhanced Data rates for Global Evolution (EDGE) that the joint optimization of the prefilter and IR produces results similar to the minimum mean-square error decision-feedback equalizer prefilter in thermal noise, but yields gain in colored noise.

A proposal for EGPRS radio link control using link adaptation and incremental redundancy

Standardization is currently in progress to specify Enhanced Data rates for GSM Evolution (EDGE). The two components of EDGE, Enhanced Circuit-Switched Data (ECSD) and Enhanced General Packet Radio Service (EGPRS), define enhancements for circuit-mode and packet-mode data, respectively. EGPRS is also intended to provide a high-rate North American digital time division multiple access (TDMA) packet data service. To achieve higher data rates, 8-ary phase shift keying (8-PSK) modulation has been introduced. Enhanced radio link control (RLC) procedures are being defined based on link adaptation and incremental redundancy to achieve superior delay/throughput performance over a wide range of operating conditions. This paper describes a candidate proposal for (RLC) block segmentation for EGPRS that provides combined link adaptation and incremental redundancy; short, fixed-length blocks to achieve lower block error rates; seamless transition between coding schemes without loss in throughput; segmentation to provide a robust Gaussian minimum shift keying (GMSK) fallback mode; and short and extended header formats. We present performance tradeoffs for the proposed scheme. Many of the features of this proposal have been included in the EGPRS specification. We provide a brief description of the block and header formats being standardized.

An overview of EGPRS: the packet data component of EDGE

The explosive growth of the Internet and the subsequent demand for wireless data communications have led to data services being a major component in the standardisation process of many cellular mobile radio systems across the world. In GSM, the standardisation of the first phase of a new data service, initiated by the European Telecommunications Standards Institute (ETSI) and collectively known as Enhanced Data rates for GSM Evolution (EDGE), was finalised in 1999. The Enhanced Circuit Switched Data (ECSD) and Enhanced General Packet Radio Service (EGPRS) components of EDGE will enhance the existing GSM circuit-switched and packet-switched data services, respectively. This paper provides an overview of EGPRS and its performance.

Equalization concepts for EDGE

An equalization concept for the novel radio access scheme Enhanced Data rates for GSM Evolution (EDGE) is proposed by which high performance can be obtained at moderate computational complexity. Because high-level modulation is employed in EDGE, optimum equalization as usually performed in Global System for Mobile Communications (GSM) receivers is too complex and suboptimum schemes have to be considered. It is shown that delayed decision-feedback sequence estimation (DDFSE) and reduced-state sequence estimation (RSSE) are promising candidates. For various channel profiles, approximations for the bit error rate of these suboptimum equalization techniques are given and compared with simulation results for DDFSE. It turns out that a discrete-time prefilter creating a minimum-phase overall impulse response is indispensable for a favorable tradeoff between performance and complexity. Additionally, the influence of channel estimation and of the receiver input filter is investigated and the reasons for performance degradation compared to the additive white Gaussian noise channel are indicated. Finally, the overall system performance attainable with the proposed equalization concept is determined for transmission with channel coding.

Improved spatial-temporal equalization for EDGE: a fast selective-direction MMSE timing recovery algorithm and two-stage soft-output equalizer

The radio interface EDGE (Enhanced Data rates for Global Evolution) is currently being standardized as an evolutionary path from GSM and TDMA-IS136 for third-generation high-speed data wireless systems. For the EDGE system with multiple antennas, spatial-temporal equalization (STE) can reduce intersymbol interference and co-channel interference, thereby increasing the capacity and range. In this paper, we propose two new techniques to improve the performance of a previously proposed STE: a fast timing recovery algorithm for a selective time-reversal equalizer and a two-stage soft-output equalizer. The new timing recovery algorithm determines the estimated burst timing and processing direction by computing the minimum mean-square error (MMSE) for decision feedback equalizers in both the forward and reverse time directions. The two-stage soft-output equalizer is the cascade of a delayed decision-feedback sequence estimator (DDFSE) and maximum a posteriori probability (MAP) estimator. The DDFSE provides better noise variance estimation and channel truncation for the following MAP. The performance of the new STE is evaluated for the EDGE. At 10% block error rate, the two-branch receiver requires a 3-7-dB lower signal-to-interference ratio (SIR) than the previous approach. Compared with the one-branch receiver, the two-branch receiver requires a 4-dB lower SNR with noise only, and a 10-27-dB lower SIR with a single interferer.

Joint equalization and interference suppression for high data rate wireless systems

Enhanced Data Rates for Global Evolution (EDGE) is currently being standardized as an evolution of GSM in Europe and of IS-136 in the United States as an air interface for high speed data services for third generation mobile systems. In this paper, we study space-time processing for EDGE to provide interference suppression. We consider the use of two receive antennas and propose a joint equalization and diversity receiver. This receiver uses feedforward filters on each diversity branch to perform minimum mean-square error cochannel interference suppression, while leaving the intersymbol interference to be mitigated by the subsequent equalizer. The equalizer is a delayed decision feedback sequence estimator, consisting of a reduced-state Viterbi processor and a feedback filter. The equalizer provides soft output to the channel decoder after deinterleaving. We describe a novel weight generation algorithm and present simulation results on the link performance of EDGE with interference suppression. These results show a significant improvement in the signal-to-interference ratio (SIR) performance due to both diversity (against fading) and interference suppression. At a 10% block error rate, the proposed receiver provides a 20 dB improvement in SIR for both the typical urban and hilly terrain profiles.

Equalisation for EDGE mobile communications

An equalisation concept for the novel radio access scheme enhanced data rates for GSM evolution (EDGE) is proposed, by which high performance can be obtained at moderate computational complexity. Because high-level modulation is employed in EDGE, optimum equalisation as performed in most GSM receivers is too complex, and suboptimum schemes have to be considered. It is shown that delayed decision-feedback sequence estimation (DDFSE) is a promising candidate. For various channel profiles, approximations for the bit error rate of DDFSE are given and compared with simulation results. It turns out that a discrete-time allpass prefilter creating a minimum-phase overall impulse response is indispensable for obtaining a favourable tradeoff between performance and complexity. Additionally, the influence of the receiver input filter is investigated.