The Experts below are selected from a list of 204 Experts worldwide ranked by ideXlab platform

Witold A Krzymien - One of the best experts on this subject based on the ideXlab platform.

  • A Null-Subcarrier-Aided Reference Symbol Mapping Scheme for 3GPP LTE Downlink in High-Mobility Scenarios
    IEEE Transactions on Vehicular Technology, 2012
    Co-Authors: Muruganathan Siva, Witold A Krzymien, Abu B. Sesay
    Abstract:

    In this paper, a new Reference Symbol (RS) mapping scheme for the Third-Generation Partnership Project (3GPP) long-term evolution (LTE) and LTE-Advanced (LTE-A) downlink is proposed to improve channel estimation performance in high-mobility communication scenarios. The proposed scheme employs null subcarriers to guard RSs, which helps mitigate the effect of intercarrier interference (ICI) on subcarriers carrying RSs. Additionally, the proposed scheme allows the ICI gain parameters to be estimated via a simple frequency-domain estimator. Modified Cramer-Rao bound (MCRB) expressions are derived for the proposed scheme, as well as for the conventional RS mapping scheme defined in the 3GPP LTE and LTE-A standards to compare their performance at high mobile user speeds. These bounds, together with mean square errors obtained from simulations, reveal superior performance achieved by the proposed scheme in high-mobility scenarios. Additionally, at high mobile user speeds, the proposed scheme offers significant bit-error-rate (BER) performance improvement over the standard RS mapping.

  • null sub carrier aided Reference Symbol mapping for improved channel estimation in 3gpp lte downlink
    Vehicular Technology Conference, 2010
    Co-Authors: Siva Muruganathan, Witold A Krzymien, A B Sesay
    Abstract:

    In this paper, a new Reference Symbol mapping scheme is proposed to improve downlink channel estimation performance over the standard Reference Symbol mapping scheme defined in the 3GPP LTE standard. The proposed scheme is based on the concept of guarding Reference Symbols (i.e., pilot Symbols) with null sub-carriers. This helps mitigate the effect of inter-carrier interference (ICI) at pilot sub-carriers. In addition, the proposed scheme allows the ICI gain parameters to be estimated via a simple estimator. To assess the relative merits of the proposed Reference Symbol mapping scheme over the standard scheme, we compare normalized mean square error and uncoded bit error rate performances of the two schemes under different mobile user speeds. These comparisons show excellent performance improvements achieved by the proposed scheme over the standard one at high mobile user speeds.

  • VTC Spring - Null Sub-Carrier Aided Reference Symbol Mapping for Improved Channel Estimation in 3GPP LTE Downlink
    2010 IEEE 71st Vehicular Technology Conference, 2010
    Co-Authors: Muruganathan Siva, Witold A Krzymien, Abu B. Sesay
    Abstract:

    In this paper, a new Reference Symbol mapping scheme is proposed to improve downlink channel estimation performance over the standard Reference Symbol mapping scheme defined in the 3GPP LTE standard. The proposed scheme is based on the concept of guarding Reference Symbols (i.e., pilot Symbols) with null sub-carriers. This helps mitigate the effect of inter-carrier interference (ICI) at pilot sub-carriers. In addition, the proposed scheme allows the ICI gain parameters to be estimated via a simple estimator. To assess the relative merits of the proposed Reference Symbol mapping scheme over the standard scheme, we compare normalized mean square error and uncoded bit error rate performances of the two schemes under different mobile user speeds. These comparisons show excellent performance improvements achieved by the proposed scheme over the standard one at high mobile user speeds.

  • Reference Symbol Assisted Multi-Stage Successive Interference Cancellation for CDMA Wireless Communication: Robustness toParameter Imperfectionswith Biphase and Quadriphase spreading
    Wireless Personal Communications, 1998
    Co-Authors: A.c.k. Soong, Witold A Krzymien
    Abstract:

    This paper investigates the sensitivity to system imperfections of a Reference Symbol assisted multi-stage successive interference cancelling (RAMSIC) receiver. Reverse link of a CDMA system with binary antipodal modulation and coherent detection is considered. Performance of systems using either biphase and quadriphase spreading is compared under different operating conditions. Analysis of a conventional matched filter receiver operating on an AWGN channel reveals that when the number of users is small (such that the multiple access interference cannot be accurately modelled as Gaussian), quadriphase spreading has a significant advantage over biphase spreading. This advantage, however, disappears when the number of users per sector is large (of the order necessary for the multiple access interference to be considered Gaussian). Results for the RAMSIC receiver with quadriphase spreading, on the other hand, show that for hexagonal cell geometry with path loss exponent of 4 and without any forward error correction coding, the traffic capacity is between 1.17 and 1.67 times that of the IS-95. These numbers represent a significant increase over those obtained with biphase spreading. Further investigation with nonidealized cell geometries and other path loss exponents also shows substantial capacity improvement over that of conventional correlator receivers. Performance losses due to nonideal transmitter power amplifier gating, imperfect power control and synchronization errors in the RAKE receiver are also determined. The results for biphase spreading show that for path loss exponent of 4, imperfect amplifier gating causes relatively minor decrease in the traffic capacity, while no such effect is observed for path loss exponents of 2 and 3. As expected, relaxing of power control for both biphase and quadriphase spreading has a similar capacity reducing effect. In spite of these two effects the resultant capacity is still significantly higher than that with the conventional matched filter receiver. Capacity increase with quadriphase over biphase spreading is between 1.4 and 2.0 times. Chip synchronization errors of the order to be expected in a properly designed conventional CDMA system have only minimal effect on performance. Therefore, we conclude that conventional synchronization algorithms should perform adequately with successive interference cancelling receivers considered in the paper.

  • A novel CDMA multiuser interference cancellation receiver with Reference Symbol aided estimation of channel parameters
    IEEE Journal on Selected Areas in Communications, 1996
    Co-Authors: A.c.k. Soong, Witold A Krzymien
    Abstract:

    A novel multistage successive interference cancellation scheme is proposed which operates on the reverse code-division multiple-access (CDMA) link using binary phase shift keying (BPSK) modulation, coherent detection and Reference Symbols to obtain channel estimates. The results of a single cell multiuser investigation demonstrate increased traffic capacity. However, this increase is initially very moderate due to corruption of the channel estimates by interference from Symbols not yet demodulated and cancelled. A modification in the transmitted signal structure addressing this problem is proposed. The results of a single cell analysis of the modified cancellation scheme demonstrate that the system's traffic capacity reaches approximately 80% of that of a multistage successive interference cancelling receiver operating with the perfect knowledge of channel parameters. A subsequent multicell investigation shows that for a hexagonal cell geometry with a path loss exponent of four and without any forward error correction (FEC) coding or cell sectorization, the system capacity compares very favorably with that of the IS-95 system, which employs powerful error control coding. Capacities with other path loss exponents and cell geometries are also investigated. The results show a substantial traffic capacity increase over that of a comparable receiver without interference cancellation.

A.c.k. Soong - One of the best experts on this subject based on the ideXlab platform.

  • Reference Symbol Assisted Multi-Stage Successive Interference Cancellation for CDMA Wireless Communication: Robustness to Parameter Imperfections with Biphase and Quadriphase spreading
    Wireless Personal Communications, 1998
    Co-Authors: A.c.k. Soong, W.a. Krzymien
    Abstract:

    This paper investigates the sensitivity to system imperfections of a Reference Symbol assisted multi-stage successive interference cancelling (RAMSIC) receiver. Reverse link of a CDMA system with binary antipodal modulation and coherent detection is considered. Performance of systems using either biphase and quadriphase spreading is compared under different operating conditions. Analysis of a conventional matched filter receiver operating on an AWGN channel reveals that when the number of users is small (such that the multiple access interference cannot be accurately modelled as Gaussian), quadriphase spreading has a significant advantage over biphase spreading. This advantage, however, disappears when the number of users per sector is large (of the order necessary for the multiple access interference to be considered Gaussian). Results for the RAMSIC receiver with quadriphase spreading, on the other hand, show that for hexagonal cell geometry with path loss exponent of 4 and without any forward error correction coding, the traffic capacity is between 1.17 and 1.67 times that of the IS-95. These numbers represent a significant increase over those obtained with biphase spreading. Further investigation with nonidealized cell geometries and other path loss exponents also shows substantial capacity improvement over that of conventional correlator receivers. Performance losses due to nonideal transmitter power amplifier gating, imperfect power control and synchronization errors in the RAKE receiver are also determined. The results for biphase spreading show that for path loss exponent of 4, imperfect amplifier gating causes relatively minor decrease in the traffic capacity, while no such effect is observed for path loss exponents of 2 and 3. As expected, relaxing of power control for both biphase and quadriphase spreading has a similar capacity reducing effect. In spite of these two effects the resultant capacity is still significantly higher than that with the conventional matched filter receiver. Capacity increase with quadriphase over biphase spreading is between 1.4 and 2.0 times. Chip synchronization errors of the order to be expected in a properly designed conventional CDMA system have only minimal effect on performance. Therefore, we conclude that conventional synchronization algorithms should perform adequately with successive interference cancelling receivers considered in the paper.

  • Reference Symbol Assisted Multi-Stage Successive Interference Cancellation for CDMA Wireless Communication: Robustness toParameter Imperfectionswith Biphase and Quadriphase spreading
    Wireless Personal Communications, 1998
    Co-Authors: A.c.k. Soong, Witold A Krzymien
    Abstract:

    This paper investigates the sensitivity to system imperfections of a Reference Symbol assisted multi-stage successive interference cancelling (RAMSIC) receiver. Reverse link of a CDMA system with binary antipodal modulation and coherent detection is considered. Performance of systems using either biphase and quadriphase spreading is compared under different operating conditions. Analysis of a conventional matched filter receiver operating on an AWGN channel reveals that when the number of users is small (such that the multiple access interference cannot be accurately modelled as Gaussian), quadriphase spreading has a significant advantage over biphase spreading. This advantage, however, disappears when the number of users per sector is large (of the order necessary for the multiple access interference to be considered Gaussian). Results for the RAMSIC receiver with quadriphase spreading, on the other hand, show that for hexagonal cell geometry with path loss exponent of 4 and without any forward error correction coding, the traffic capacity is between 1.17 and 1.67 times that of the IS-95. These numbers represent a significant increase over those obtained with biphase spreading. Further investigation with nonidealized cell geometries and other path loss exponents also shows substantial capacity improvement over that of conventional correlator receivers. Performance losses due to nonideal transmitter power amplifier gating, imperfect power control and synchronization errors in the RAKE receiver are also determined. The results for biphase spreading show that for path loss exponent of 4, imperfect amplifier gating causes relatively minor decrease in the traffic capacity, while no such effect is observed for path loss exponents of 2 and 3. As expected, relaxing of power control for both biphase and quadriphase spreading has a similar capacity reducing effect. In spite of these two effects the resultant capacity is still significantly higher than that with the conventional matched filter receiver. Capacity increase with quadriphase over biphase spreading is between 1.4 and 2.0 times. Chip synchronization errors of the order to be expected in a properly designed conventional CDMA system have only minimal effect on performance. Therefore, we conclude that conventional synchronization algorithms should perform adequately with successive interference cancelling receivers considered in the paper.

  • A novel CDMA multiuser interference cancellation receiver with Reference Symbol aided estimation of channel parameters
    IEEE Journal on Selected Areas in Communications, 1996
    Co-Authors: A.c.k. Soong, Witold A Krzymien
    Abstract:

    A novel multistage successive interference cancellation scheme is proposed which operates on the reverse code-division multiple-access (CDMA) link using binary phase shift keying (BPSK) modulation, coherent detection and Reference Symbols to obtain channel estimates. The results of a single cell multiuser investigation demonstrate increased traffic capacity. However, this increase is initially very moderate due to corruption of the channel estimates by interference from Symbols not yet demodulated and cancelled. A modification in the transmitted signal structure addressing this problem is proposed. The results of a single cell analysis of the modified cancellation scheme demonstrate that the system's traffic capacity reaches approximately 80% of that of a multistage successive interference cancelling receiver operating with the perfect knowledge of channel parameters. A subsequent multicell investigation shows that for a hexagonal cell geometry with a path loss exponent of four and without any forward error correction (FEC) coding or cell sectorization, the system capacity compares very favorably with that of the IS-95 system, which employs powerful error control coding. Capacities with other path loss exponents and cell geometries are also investigated. The results show a substantial traffic capacity increase over that of a comparable receiver without interference cancellation.

  • Effect of antenna diversity on performance of Reference Symbol assisted interference cancellation in CDMA wireless systems
    Proceedings of ICUPC 97 - 6th International Conference on Universal Personal Communications, 1
    Co-Authors: A.c.k. Soong, W.a. Krzymien
    Abstract:

    This paper investigates the effect of antenna diversity on the performance of a Reference Symbol assisted multi-stage interference cancelling (RAMSIC) receiver. The uplink of a DS-CDMA system with coherent detection operating on a flat Rayleigh fading system is considered. The results show that with a realistic feedback power control algorithm, in fast fading the capacity of the system with dual receive antenna diversity can be increased 1.6 times over that of the IS-95 system. It is also demonstrated that the capacity of the system in a slow fading environment increases dramatically over that under fast fading. Therefore, the 1.6 fold advantage of the RAMSIC receiver may be interpreted as the worst case performance advantage. Investigation of transmitter antenna diversity shows that in systems requiring lower BER (10/sup -4/ or less), such as in image and video communication, artificial multipath created by two transmitting antennas increases capacity.

  • CDMA multi-user interference cancellation with Reference Symbol aided estimation of channel parameters
    IEEE Pacific Rim Conference on Communications Computers and Signal Processing. Proceedings, 1
    Co-Authors: A.c.k. Soong, Witold A Krzymien
    Abstract:

    A novel multi-stage successive interference cancellation scheme is proposed which operates on the reverse CDMA link using BPSK modulation, coherent detection and Reference Symbols to obtain channel estimates. Single user analysis shows that the performance of the coherent detector with Reference Symbols is approximately 1.5 dB worse than that of an ideal coherent receiver on Rayleigh flat fading and frequency selective fading channel. Optimization of the parameters arising in the context of system implementation was also investigated. The results of a single cell multi-user investigation show that substantial capacity improvements can be obtained with successive interference cancellation using Reference Symbol channel estimates.

W.a. Krzymien - One of the best experts on this subject based on the ideXlab platform.

  • Reference Symbol Assisted Multi-Stage Successive Interference Cancellation for CDMA Wireless Communication: Robustness to Parameter Imperfections with Biphase and Quadriphase spreading
    Wireless Personal Communications, 1998
    Co-Authors: A.c.k. Soong, W.a. Krzymien
    Abstract:

    This paper investigates the sensitivity to system imperfections of a Reference Symbol assisted multi-stage successive interference cancelling (RAMSIC) receiver. Reverse link of a CDMA system with binary antipodal modulation and coherent detection is considered. Performance of systems using either biphase and quadriphase spreading is compared under different operating conditions. Analysis of a conventional matched filter receiver operating on an AWGN channel reveals that when the number of users is small (such that the multiple access interference cannot be accurately modelled as Gaussian), quadriphase spreading has a significant advantage over biphase spreading. This advantage, however, disappears when the number of users per sector is large (of the order necessary for the multiple access interference to be considered Gaussian). Results for the RAMSIC receiver with quadriphase spreading, on the other hand, show that for hexagonal cell geometry with path loss exponent of 4 and without any forward error correction coding, the traffic capacity is between 1.17 and 1.67 times that of the IS-95. These numbers represent a significant increase over those obtained with biphase spreading. Further investigation with nonidealized cell geometries and other path loss exponents also shows substantial capacity improvement over that of conventional correlator receivers. Performance losses due to nonideal transmitter power amplifier gating, imperfect power control and synchronization errors in the RAKE receiver are also determined. The results for biphase spreading show that for path loss exponent of 4, imperfect amplifier gating causes relatively minor decrease in the traffic capacity, while no such effect is observed for path loss exponents of 2 and 3. As expected, relaxing of power control for both biphase and quadriphase spreading has a similar capacity reducing effect. In spite of these two effects the resultant capacity is still significantly higher than that with the conventional matched filter receiver. Capacity increase with quadriphase over biphase spreading is between 1.4 and 2.0 times. Chip synchronization errors of the order to be expected in a properly designed conventional CDMA system have only minimal effect on performance. Therefore, we conclude that conventional synchronization algorithms should perform adequately with successive interference cancelling receivers considered in the paper.

  • Effect of antenna diversity on performance of Reference Symbol assisted interference cancellation in CDMA wireless systems
    Proceedings of ICUPC 97 - 6th International Conference on Universal Personal Communications, 1
    Co-Authors: A.c.k. Soong, W.a. Krzymien
    Abstract:

    This paper investigates the effect of antenna diversity on the performance of a Reference Symbol assisted multi-stage interference cancelling (RAMSIC) receiver. The uplink of a DS-CDMA system with coherent detection operating on a flat Rayleigh fading system is considered. The results show that with a realistic feedback power control algorithm, in fast fading the capacity of the system with dual receive antenna diversity can be increased 1.6 times over that of the IS-95 system. It is also demonstrated that the capacity of the system in a slow fading environment increases dramatically over that under fast fading. Therefore, the 1.6 fold advantage of the RAMSIC receiver may be interpreted as the worst case performance advantage. Investigation of transmitter antenna diversity shows that in systems requiring lower BER (10/sup -4/ or less), such as in image and video communication, artificial multipath created by two transmitting antennas increases capacity.

  • Performance of a Reference Symbol assisted multi-stage successive interference cancelling receiver with quadriphase spreading
    1997 IEEE 47th Vehicular Technology Conference. Technology in Motion, 1
    Co-Authors: A.c.k. Soong, W.a. Krzymien
    Abstract:

    The performance of a multi-stage successive interference cancelling receiver using Reference Symbols to obtain channel estimates in a CDMA system is investigated with quadriphase spreading. The focus is on the reverse link of a system with binary antipodal modulation and coherent detection. The results show that for a hexagonal cell geometry with path loss exponent of 4 and without any forward error correction coding, the capacity of the system is between 1.17 and 1.67 times that of the IS-95 system. Further investigation with non-idealized cell geometries and other path loss exponents shows substantial capacity improvement over that of conventional non-interference cancelling receivers. The sensitivity of the system to power control and synchronization errors is also investigated. The results also show that relaxing the power control reduces the capacity. The capacity increase over systems with interference cancelling receivers and biphase spreading is between 1.4 and 2.0 times. Chip synchronization errors of the order to be expected in a properly designed conventional CDMA system have minimal effect on performance.

Harry H. Cheng - One of the best experts on this subject based on the ideXlab platform.

  • ICRA - VLSI architecture for hand-written Symbol recognition
    Proceedings. 1986 IEEE International Conference on Robotics and Automation, 1
    Co-Authors: Harry H. Cheng
    Abstract:

    Comparing the hand-written Symbol with the set of training Symbols (called Reference Symbols), we can recognize the input hand-written Symbol by computing the distances among the input Symbol and the Reference Symbols in the training set. In this paper we propose a VLSI architecture based on the space-time domain expansion which can compute the Symbol distance and also give the index-pairs which correspond to the warp function. The time complexity is O(max(m, n)) by using m × n processing elements array, where m is the length of the input Symbol and n is the length of the Reference Symbol. With a uniprocessor the matching process will have the time complexity O(m × n). If there are p Reference Symbols, using the proposed architecture the recognition problem can be solved in time O(max(m,n,p)). With a uniprocessor the time complexity will be O(m × n × p). The algorithm partition problems are discussed. Verification of the proposed VLSI architecture is also given.

Fuyun Ling - One of the best experts on this subject based on the ideXlab platform.

  • Coherent detection with Reference-Symbol based channel estimation for direct sequence CDMA uplink communications
    IEEE 43rd Vehicular Technology Conference, 1
    Co-Authors: Fuyun Ling
    Abstract:

    A new coding/modulation arrangement for up-link direct-sequence code division multiple access (DS-CDMA) communication, which employs coherent detection with Reference-Symbol based channel estimation, is presented. It is shown that the required E/sub b//N/sub O/ for this scheme is about 2 dB to 2.5 dB lower than non-coherent detection of Walsh coding with bit interleaving and about 1 dB to 1.3 dB lower than noncoherent detection with Walsh Symbol interleaving over the entire range of practical vehicle speeds. A frequency domain analysis of this scheme is given.

  • Implementation of a coherent reverse channel 900 MHz CDMA receiver with Reference Symbols
    Proceedings IEEE International Conference on Communications ICC '95, 1
    Co-Authors: T.a. Sexton, Fuyun Ling
    Abstract:

    There are many radio access standards contending for attention in the world-wide cellular marketplace. Practical estimator methods and sequences are introduced for the Reference Symbol based DS-CDMA radio (denoted "RC"). It is a physical layer scheme involving insertion of a known training sequence into the coded, interleaved bit stream for an IS-95-like CDMA reverse channel. This paper presents the principle estimators needed for implementation of an RC receiver, and frame error rate (FER) results for a flat fading channel. The frame error rate or Eb/No required for a 1% FER is given for both idealized and realistic conditions concerning time varying carrier frequency offset and delay slew of the received timing. A comparison to IS-95 shows a 2 dB improvement.