Proceedings of 1994 28th Asilomar Conference on Signals, Systems and Computers
ABSTRACT In a wireless communication environment, multi-path propagation and mobile user motion r... more ABSTRACT In a wireless communication environment, multi-path propagation and mobile user motion result in a dispersive time-varying communication channel. In order to analyze the performance of wireless com-munication systems. it is rieressary to define models which reasonably ...
IEEE International Symposium on Circuits and Systems, 2001
A finite-length optimized-delay multi-input multi-output mean-square-error decision-feedback equa... more A finite-length optimized-delay multi-input multi-output mean-square-error decision-feedback equalizer for space-time block-coded transmission over multipath fading channels is presented. Alamouti's space-time block code with 2 transmit and 2 receive antenna on a typical urban EDGE channel is taken as a case study. We propose a combined equalization and decoding scheme under the constraint of linear processing complexity (no trellis search) at the receiver. Performance comparisons are made with the single-transmit/single-receive antenna case and the case of multi-input multi-output feedforward linear equalization only with no decision feedback
International Conference on Acoustics, Speech, and Signal Processing, 1994
Mobile radio channels can be generally characterized as a fading multipath channel with multipath... more Mobile radio channels can be generally characterized as a fading multipath channel with multipath spread delay that ranges from a few microseconds (μs) up to as much as 15 μs. Such large delays result in intersymbol interference which raises the need for equalization. A semi-blind maximum likelihood sequence estimation (MLSE) with an antenna array is studied as an adaptive equalization method for time division multiple access (TDMA) digital cellular systems. The MLSE is implemented using a Viterbi algorithm (VA). An antenna array is used to utilize both temporal and spatial structure in the received signal to provide the VA with the estimate of the channel impulse response necessary for it to perform MLSE
Wireless Communications and Mobile Computing, 2001
The information capacity of wireless communication systems can be increased dramatically by emplo... more The information capacity of wireless communication systems can be increased dramatically by employing multiple transmit and receive antennas [Foschini GJ, Gans MJ. On limits of wireless communications in a fading environment when using multiple antennas. An effective approach to increasing data rate over wireless channels is to employ coding techniques appropriate to multiple transmit antennas, that is space-time coding. Space-time codes introduce temporal and spatial correlation into signals transmitted from different antennas, in order to provide diversity at the receiver, and coding gain over an uncoded system. The spatial-temporal structure of these codes can be exploited to further increase the capacity of wireless systems with a relatively simple receiver structure. This paper provides an overview of space-time coding techniques and the associated signal processing framework.
Exploring the temporal and spatial domains both at the receiver and transmitter offers important ... more Exploring the temporal and spatial domains both at the receiver and transmitter offers important means for considerably improving the system performance in cellular networks. In this paper, the impact of using open-loop transmit diversity based on space-time block codes in a multi-user DS-CDMA system operating in a frequency selective fading environment is explored. A non-joint linear multi-user detection and space-time
IEEE International Conference on Communications, 1997
We consider the problem of receiving CDMA multipath signals at a receiver with an antenna array. ... more We consider the problem of receiving CDMA multipath signals at a receiver with an antenna array. We derive the space-time matched filter for the multipath signals arriving at the array and show that this space-time matched filter consists of a front-end spatial matched filter or a bank of beamformers (one for each multipath component), followed by a temporal matched filter, or a bank of correlators (one for each multipath component). Then we derive the optimum (maximum likelihood) sequence detector that can be implemented via a Viterbi algorithm. We also present a sub-optimal space-time decorrelating receiver structure and discuss its limitations. Based on this space-time matched filter framework, we briefly discuss conventional space-time receiver structures for CDMA multipath signals. Analysis results for a space-time receiver with DPSK signaling show improved bit error rate performance due to the exploitation of the spatial dimension in the received signal
Global Telecommunications Conference, . GLOBECOM . IEEE, 1994
In this paper, we evaluate the uplink capacity of a CDMA cellular system using DPSK modulation wi... more In this paper, we evaluate the uplink capacity of a CDMA cellular system using DPSK modulation with antenna array at base-station. A 2D-RAKE receiver structure with predetection equal gain combining is used for demodulation. We study both outage and blocking probabilities of the system as a function of cell loading and number of array elements. Assuming perfect instantaneous power control and considering the effects of shadowing, multipath fading, path loss, and voice activity, we evaluate the system capacity in terms of the number of users per cell. Simulation results are also presented.
Global Telecommunications Conference, . GLOBECOM . IEEE, 2000
Diversity transmission at the base station is an effective technique to combat the adverse effect... more Diversity transmission at the base station is an effective technique to combat the adverse effects of fading. This is suggested as an alternative to diversity at the terminal, thereby reducing the implementation complexity. Space-time coding has been proposed as a coding technique for diversity transmission that will provide additional performance gains. We describe a maximum likelihood sequence estimator (MLSE) for space-time coded signals that exploits the structure present in some of these codes. Simulation results of the proposed equalizer show a substantial improvement over single antenna transmission
IEEE International Conference on Communications, 2003
Diversity transmission at the base station is an effective technique to combat adverse effects of... more Diversity transmission at the base station is an effective technique to combat adverse effects of fading. This is suggested as an alternative to diversity at the terminal, thereby reducing the implementation complexity. In this paper, we present a transmission scheme that combines space-time block coding over frequency selective channels with single carrier frequency domain interference suppression and equalization. It is shown that this scheme will provide the diversity benefit of both the frequency selective channel and the space-time block code while completely suppressing the interference from another co-channel transmitter that occupies exactly the same channel (time & frequency) as the desired transmitter.
IEEE International Conference on Communications, 2001
Diversity transmission at the base station is an effective technique to combat the adverse effect... more Diversity transmission at the base station is an effective technique to combat the adverse effects of fading. This is suggested as an alternative to diversity at the terminal, thereby reducing the implementation complexity. We evaluate the matched filter bound (MFB) for two transmit diversity schemes with two transmit antennas: delay diversity and space-time block coding. Theoretical results show that even though the expected value of the matched filter bound is the same for both approaches, the diversity order exhibited by the space-time block coding approach is larger than that of delay diversity for any frequency selective channel with more than 1 tap. In fact for a frequency selective channel with L+1 taps with equal energy, the diversity order exhibited by the space-time coding MFB is 2×(L+1) while that of delay diversity is L+2
The rapid increase in the number of mobile telephone users has put great pressure on system capac... more The rapid increase in the number of mobile telephone users has put great pressure on system capacity in many urban areas. This is despite the range of technologies that have multiplied the capacity including the most recently use of digital communication and coding. Antenna arrays at the base-station have been recently shown to increase system capacity. We study the performance of the downlink channel and predict capacity improvement. We also present simulation results to support our analysis
IEEE International Conference on Communications, 1995
The increasing demand for mobile communication services without corresponding increases in RF spe... more The increasing demand for mobile communication services without corresponding increases in RF spectrum allocation requires new techniques to improve spectrum utilization. Spatial processing using antenna arrays at the base-station has been proposed to reduce co-channel interference and reduce fading of the desired signal, leading to an increase in system capacity. The use of base station antenna, arrays in wireless CDMA is studied. A recursive, fast, and numerically stable algorithm estimating the array response vector and the optimum beamforming weights is derived. Our approach uses a space-time processing approach for estimating-the array response vector, and hence the optimum beamforming weights. Simulation results are also presented
Code division multiple access (CDMA) has been shown to offer higher capacity than the existing FD... more Code division multiple access (CDMA) has been shown to offer higher capacity than the existing FDMA or TDMA systems. Since no pilot is used in the reverse link for power efficiency considerations, M-ary orthogonal modulation with noncoherent reception is a suitable modulation technique. Spatial processing with base-station antenna arrays was previously proposed for improving coverage and increasing system capacity. The present authors study the performance of a base-station antenna arrays receiver structure for M-ary orthogonal modulation and noncoherent RAKE combining in the presence of multipath
Wireless Communications and Mobile Computing, 2001
The information capacity of wireless communication systems can be increased dramatically by emplo... more The information capacity of wireless communication systems can be increased dramatically by employing multiple transmit and receive antennas [Foschini GJ, Gans MJ. On limits of wireless communications in a fading environment when using multiple antennas. An effective approach to increasing data rate over wireless channels is to employ coding techniques appropriate to multiple transmit antennas, that is space-time coding. Space-time codes introduce temporal and spatial correlation into signals transmitted from different antennas, in order to provide diversity at the receiver, and coding gain over an uncoded system. The spatial-temporal structure of these codes can be exploited to further increase the capacity of wireless systems with a relatively simple receiver structure. This paper provides an overview of space-time coding techniques and the associated signal processing framework.
IEEE International Conference on Communications, 1997
We consider the design of channel codes for improving the data rate and/or the reliability of com... more We consider the design of channel codes for improving the data rate and/or the reliability of communications over fading channels using multiple transmit antennas. Data is encoded by a channel code and the encoded data is split into n streams that are simultaneously transmitted using n transmit antennas. The received signal at each receive antenna is a linear superposition of the n transmitted signals perturbed by noise. We derive performance criteria for designing such codes under the assumption that the fading is slow and frequency nonselective. Performance is shown to be determined by matrices constructed from pairs of distinct code sequences. The minimum rank among these matrices quantifies the diversity gain, while the minimum determinant of these matrices quantifies the coding gain. The results are then extended to fast fading channels. The design criteria are used to design trellis codes for high data rate wireless communication. The encoding/decoding complexity of these codes is comparable to trellis codes employed in practice over Gaussian channels. The codes constructed here provide the best tradeoff between data rate, diversity advantage, and trellis complexity. Simulation results are provided for 4 and 8 PSK signal sets with data rates of 2 and 3 bits/symbol, demonstrating excellent performance that is within 2-3 dB of the outage capacity for these channels using only 64 state encoders.
Proceedings of 1994 28th Asilomar Conference on Signals, Systems and Computers
ABSTRACT In a wireless communication environment, multi-path propagation and mobile user motion r... more ABSTRACT In a wireless communication environment, multi-path propagation and mobile user motion result in a dispersive time-varying communication channel. In order to analyze the performance of wireless com-munication systems. it is rieressary to define models which reasonably ...
IEEE International Symposium on Circuits and Systems, 2001
A finite-length optimized-delay multi-input multi-output mean-square-error decision-feedback equa... more A finite-length optimized-delay multi-input multi-output mean-square-error decision-feedback equalizer for space-time block-coded transmission over multipath fading channels is presented. Alamouti's space-time block code with 2 transmit and 2 receive antenna on a typical urban EDGE channel is taken as a case study. We propose a combined equalization and decoding scheme under the constraint of linear processing complexity (no trellis search) at the receiver. Performance comparisons are made with the single-transmit/single-receive antenna case and the case of multi-input multi-output feedforward linear equalization only with no decision feedback
International Conference on Acoustics, Speech, and Signal Processing, 1994
Mobile radio channels can be generally characterized as a fading multipath channel with multipath... more Mobile radio channels can be generally characterized as a fading multipath channel with multipath spread delay that ranges from a few microseconds (μs) up to as much as 15 μs. Such large delays result in intersymbol interference which raises the need for equalization. A semi-blind maximum likelihood sequence estimation (MLSE) with an antenna array is studied as an adaptive equalization method for time division multiple access (TDMA) digital cellular systems. The MLSE is implemented using a Viterbi algorithm (VA). An antenna array is used to utilize both temporal and spatial structure in the received signal to provide the VA with the estimate of the channel impulse response necessary for it to perform MLSE
Wireless Communications and Mobile Computing, 2001
The information capacity of wireless communication systems can be increased dramatically by emplo... more The information capacity of wireless communication systems can be increased dramatically by employing multiple transmit and receive antennas [Foschini GJ, Gans MJ. On limits of wireless communications in a fading environment when using multiple antennas. An effective approach to increasing data rate over wireless channels is to employ coding techniques appropriate to multiple transmit antennas, that is space-time coding. Space-time codes introduce temporal and spatial correlation into signals transmitted from different antennas, in order to provide diversity at the receiver, and coding gain over an uncoded system. The spatial-temporal structure of these codes can be exploited to further increase the capacity of wireless systems with a relatively simple receiver structure. This paper provides an overview of space-time coding techniques and the associated signal processing framework.
Exploring the temporal and spatial domains both at the receiver and transmitter offers important ... more Exploring the temporal and spatial domains both at the receiver and transmitter offers important means for considerably improving the system performance in cellular networks. In this paper, the impact of using open-loop transmit diversity based on space-time block codes in a multi-user DS-CDMA system operating in a frequency selective fading environment is explored. A non-joint linear multi-user detection and space-time
IEEE International Conference on Communications, 1997
We consider the problem of receiving CDMA multipath signals at a receiver with an antenna array. ... more We consider the problem of receiving CDMA multipath signals at a receiver with an antenna array. We derive the space-time matched filter for the multipath signals arriving at the array and show that this space-time matched filter consists of a front-end spatial matched filter or a bank of beamformers (one for each multipath component), followed by a temporal matched filter, or a bank of correlators (one for each multipath component). Then we derive the optimum (maximum likelihood) sequence detector that can be implemented via a Viterbi algorithm. We also present a sub-optimal space-time decorrelating receiver structure and discuss its limitations. Based on this space-time matched filter framework, we briefly discuss conventional space-time receiver structures for CDMA multipath signals. Analysis results for a space-time receiver with DPSK signaling show improved bit error rate performance due to the exploitation of the spatial dimension in the received signal
Global Telecommunications Conference, . GLOBECOM . IEEE, 1994
In this paper, we evaluate the uplink capacity of a CDMA cellular system using DPSK modulation wi... more In this paper, we evaluate the uplink capacity of a CDMA cellular system using DPSK modulation with antenna array at base-station. A 2D-RAKE receiver structure with predetection equal gain combining is used for demodulation. We study both outage and blocking probabilities of the system as a function of cell loading and number of array elements. Assuming perfect instantaneous power control and considering the effects of shadowing, multipath fading, path loss, and voice activity, we evaluate the system capacity in terms of the number of users per cell. Simulation results are also presented.
Global Telecommunications Conference, . GLOBECOM . IEEE, 2000
Diversity transmission at the base station is an effective technique to combat the adverse effect... more Diversity transmission at the base station is an effective technique to combat the adverse effects of fading. This is suggested as an alternative to diversity at the terminal, thereby reducing the implementation complexity. Space-time coding has been proposed as a coding technique for diversity transmission that will provide additional performance gains. We describe a maximum likelihood sequence estimator (MLSE) for space-time coded signals that exploits the structure present in some of these codes. Simulation results of the proposed equalizer show a substantial improvement over single antenna transmission
IEEE International Conference on Communications, 2003
Diversity transmission at the base station is an effective technique to combat adverse effects of... more Diversity transmission at the base station is an effective technique to combat adverse effects of fading. This is suggested as an alternative to diversity at the terminal, thereby reducing the implementation complexity. In this paper, we present a transmission scheme that combines space-time block coding over frequency selective channels with single carrier frequency domain interference suppression and equalization. It is shown that this scheme will provide the diversity benefit of both the frequency selective channel and the space-time block code while completely suppressing the interference from another co-channel transmitter that occupies exactly the same channel (time & frequency) as the desired transmitter.
IEEE International Conference on Communications, 2001
Diversity transmission at the base station is an effective technique to combat the adverse effect... more Diversity transmission at the base station is an effective technique to combat the adverse effects of fading. This is suggested as an alternative to diversity at the terminal, thereby reducing the implementation complexity. We evaluate the matched filter bound (MFB) for two transmit diversity schemes with two transmit antennas: delay diversity and space-time block coding. Theoretical results show that even though the expected value of the matched filter bound is the same for both approaches, the diversity order exhibited by the space-time block coding approach is larger than that of delay diversity for any frequency selective channel with more than 1 tap. In fact for a frequency selective channel with L+1 taps with equal energy, the diversity order exhibited by the space-time coding MFB is 2×(L+1) while that of delay diversity is L+2
The rapid increase in the number of mobile telephone users has put great pressure on system capac... more The rapid increase in the number of mobile telephone users has put great pressure on system capacity in many urban areas. This is despite the range of technologies that have multiplied the capacity including the most recently use of digital communication and coding. Antenna arrays at the base-station have been recently shown to increase system capacity. We study the performance of the downlink channel and predict capacity improvement. We also present simulation results to support our analysis
IEEE International Conference on Communications, 1995
The increasing demand for mobile communication services without corresponding increases in RF spe... more The increasing demand for mobile communication services without corresponding increases in RF spectrum allocation requires new techniques to improve spectrum utilization. Spatial processing using antenna arrays at the base-station has been proposed to reduce co-channel interference and reduce fading of the desired signal, leading to an increase in system capacity. The use of base station antenna, arrays in wireless CDMA is studied. A recursive, fast, and numerically stable algorithm estimating the array response vector and the optimum beamforming weights is derived. Our approach uses a space-time processing approach for estimating-the array response vector, and hence the optimum beamforming weights. Simulation results are also presented
Code division multiple access (CDMA) has been shown to offer higher capacity than the existing FD... more Code division multiple access (CDMA) has been shown to offer higher capacity than the existing FDMA or TDMA systems. Since no pilot is used in the reverse link for power efficiency considerations, M-ary orthogonal modulation with noncoherent reception is a suitable modulation technique. Spatial processing with base-station antenna arrays was previously proposed for improving coverage and increasing system capacity. The present authors study the performance of a base-station antenna arrays receiver structure for M-ary orthogonal modulation and noncoherent RAKE combining in the presence of multipath
Wireless Communications and Mobile Computing, 2001
The information capacity of wireless communication systems can be increased dramatically by emplo... more The information capacity of wireless communication systems can be increased dramatically by employing multiple transmit and receive antennas [Foschini GJ, Gans MJ. On limits of wireless communications in a fading environment when using multiple antennas. An effective approach to increasing data rate over wireless channels is to employ coding techniques appropriate to multiple transmit antennas, that is space-time coding. Space-time codes introduce temporal and spatial correlation into signals transmitted from different antennas, in order to provide diversity at the receiver, and coding gain over an uncoded system. The spatial-temporal structure of these codes can be exploited to further increase the capacity of wireless systems with a relatively simple receiver structure. This paper provides an overview of space-time coding techniques and the associated signal processing framework.
IEEE International Conference on Communications, 1997
We consider the design of channel codes for improving the data rate and/or the reliability of com... more We consider the design of channel codes for improving the data rate and/or the reliability of communications over fading channels using multiple transmit antennas. Data is encoded by a channel code and the encoded data is split into n streams that are simultaneously transmitted using n transmit antennas. The received signal at each receive antenna is a linear superposition of the n transmitted signals perturbed by noise. We derive performance criteria for designing such codes under the assumption that the fading is slow and frequency nonselective. Performance is shown to be determined by matrices constructed from pairs of distinct code sequences. The minimum rank among these matrices quantifies the diversity gain, while the minimum determinant of these matrices quantifies the coding gain. The results are then extended to fast fading channels. The design criteria are used to design trellis codes for high data rate wireless communication. The encoding/decoding complexity of these codes is comparable to trellis codes employed in practice over Gaussian channels. The codes constructed here provide the best tradeoff between data rate, diversity advantage, and trellis complexity. Simulation results are provided for 4 and 8 PSK signal sets with data rates of 2 and 3 bits/symbol, demonstrating excellent performance that is within 2-3 dB of the outage capacity for these channels using only 64 state encoders.
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