Abstract: Pilot symbol assisted modulation (PSAM) techniques for Rayleigh and Rician fading channels are derived. Previous techniques implement PSAM signal detectors as an ad-hoc design, using pilot symbols to first estimate channel gain, and then using channel gain estimates in a conventional coherent detector to make data decisions. Although this structure may be effective for binary phase shift keying in Rayleigh fading, it is suboptimal for Rician fading and for 16-ary quadrature amplitude modulation in Rayleigh fading. According to techniques disclosed herein, a PSAM signal detector jointly processes pilot symbols and data symbols. The performance of signal detectors according to embodiments of the invention is analyzed and compared with that of conventional detectors. Numerical results are presented to show that the performance gain of a proposed new PSAM signal detector over conventional PSAM detectors can be as much as 2 or 3 dB for Rician fading in some cases.

Abstract: A novel ultra-wide bandwidth receiver structure dubbed the “zonal” receiver is proposed to detect time-hopping ultra-wide bandwidth signals in multiple access interference channels. The zonal receiver outperforms the conventional matched filter ultra-wide bandwidth receiver and the recently proposed soft-limiting ultra-wide bandwidth receiver when only MAI is present, or AWGN is negligible compared to MAI. In more practical mixed MAI-plus-AWGN environments, the zonal ultra-wide bandwidth receiver achieves better performance than the conventional matched filter ultra-wide bandwidth receiver, the recently proposed soft-limiting ultra-wide bandwidth receiver, and the recently proposed adaptive threshold soft-limiting ultra-wide bandwidth receiver. In multipath fading UWB channels, a new Rake receiver based on the zonal UWB receiver design has been proposed, this new Rake receiver can achieve better BER performance than the conventional matched filter based Rake receiver.

Abstract: Two hybrid message decoders for low-density parity-check (LDPC) codes are proposed. One decoder uses a posteriori probability ratio (APPR) and a posteriori probability difference (APPD), and the other decoder uses a logarithm a posteriori probability ratio (LAPPR) and a logarithm a posteriori probability difference (LAPPD) as hybrid message. Since the variable node and check node processing can be readily done using APPR and APPD, respectively, the proposed decoders have lower complexity than the conventional decoder that uses LAPPR only as a message.

Abstract: A novel receiver structure is proposed for detecting a time-hopping ultra-wide bandwidth signal in the presence of multiple access interference. The proposed structure achieves better bit error rate performance than the conventional matched receiver when operating in multiple access interference. When operating in a multiple access interference-plus-Gaussian-noise environment, the receiver structure outperforms the conventional matched filter receiver for moderate to large values of signal-to-noise ratio. A receiver structure with adaptive limiting threshold is further proposed to ensure the performance of the soft-limiting receiver always meets or surpasses the performance of the conventional UWB receiver for all values of signal-to-noise ratio.

Abstract: A discrete cosine transform (DCT)-based orthogonal frequency-division multiplexing (OFDM) system is provided with a zero-padding guard interval and MMSE reception. The performance of the DCT-OFDM system with the zero-padding guard interval scheme and the minimum mean-square error (MMSE) receiver over time-varying multipath Rayleigh fading channels is investigated. The results show that employing the proposed DCT-OFDM system rather than the conventional DFT-OFDM system can provide better bit error rate performance in practical systems, by as much as 6 dB in signal-to-noise ratio.

Abstract: Novel non-data-aided maximum likelihood estimators for the delays and the attenuations in an ultra-wide bandwidth channel are proposed. Numerical results show that these new estimators outperform the previous non-data-aided maximum likelihood channel estimators derived in the literature. Moreover, in some cases, the performances of the new non-data-aided estimators approach those of the data-aided estimators, enabling us to reduce the overhead expense of pilot symbols.

Abstract: Space-time code, and methods for constructing space-time codes are provided. The space-time coder performs a respective linear transformation on each of P sets of K modulated symbols of a modulated symbol stream to produce P sets of T linearly transformed symbols, applies a respective phase rotation to each set of T linearly transformed symbols to produce a respective set of T phase rotated symbols, and performs a threading operation on the sets of T phase rotated symbols to produce P threaded sequences that define M output sequences. During each of T symbol periods, a respective one of the P threaded sequences includes a symbol from one of the P sets of phase rotated symbols. At least one symbol from each set of phase rotated symbols appears in each output sequence, where M>=2, 2<=P<=M, and T>=M and M>=K.

Abstract: A novel ultra-wide bandwidth receiver structure dubbed the “zonal” receiver is proposed to detect time-hopping ultra-wide bandwidth signals in multiple access interference channels. The zonal receiver outperforms the conventional matched filter ultra-wide bandwidth receiver and the recently proposed soft-limiting ultra-wide bandwidth receiver when only MAI is present, or AWGN is negligible compared to MAI. In more practical mixed MAI-plus-AWGN environments, the zonal ultra-wide bandwidth receiver achieves better performance than the conventional matched filter ultra-wide bandwidth receiver, the recently proposed soft-limiting ultra-wide bandwidth receiver, and the recently proposed adaptive threshold soft-limiting ultra-wide bandwidth receiver. In multipath fading UWB channels, a new Rake receiver based on the zonal UWB receiver design has been proposed, this new Rake receiver can achieve better BER performance than the conventional matched filter based Rake receiver.

Abstract: Two hybrid message decoders for low-density parity-check (LDPC) codes are proposed. One decoder uses a posteriori probability ratio (APPR) and a posteriori probability difference (APPD), and the other decoder uses a logarithm a posteriori probability ratio (LAPPR) and a logarithm a posteriori probability difference (LAPPD) as hybrid message. Since the variable node and check node processing can be readily done using APPR and APPD, respectively, the proposed decoders have lower complexity than the conventional decoder that uses LAPPR only as a message.

Abstract: A dual-branch decorrelator receiver is provided in which decorrelation is performed with a simple addition and subtraction. The same receiver finds application in pre-processing signals that may not be correlated.

Abstract: A UWB receiver dubbed the “p-order metric” receiver (p-omr) is proposed to detect the time-hopping ultra-wide bandwidth signal in multiple access interference channels. The receiver acquires a signal over a wireless channel, adaptively selects a shaping parameter, p, over time and generates a first set of partial statistics by, for each of a plurality N of observations per symbol, using the shaping parameter to modify the exponential order of the approximation of the noise plus multiple access interference probability density function, f(x), used in the receiver model.

Abstract: A novel receiver structure is proposed for detecting a time-hopping ?ltrat-wide bandwidth signal in the presence of multiple access interference. The proposed structure achieves better bit error rate performance than the conventional matched receiver when operating in multiple access interference. When operating in a multiple access interference-plus-Gaussian-noise environment, the receiver structure outperforms the conventional matched filter receiver for moderate to large values of signal-to-noise ratio. A receiver structure with adaptive limiting threshold is further proposed to ensure the performance of the soft-limiting receiver always meets or surpasses the performance of the conventional UWB receiver for all values of signal-to-noise ratio.

Abstract: Space-time code, and methods for constructing space-time codes are provided.

Abstract: Time variation on fading channels hinders accurate channel estimation in differential space-time modulation and deteriorates the performance. Decision-feedback differential detection is employed for block differential space-time modulation, and compared with conventional differential space-time modulation. It is observed that the proposed scheme does not suffer effective fading bandwidth expansion, as does the conventional scheme. An improved effective signal-to-noise ratio approach is proposed for analyzing the performance of the proposed scheme in time-varying flat Rayleigh fading. Theoretical analysis and simulations show the improved performance of the proposed scheme over the conventional scheme.

Abstract: Space-time code, and methods for constructing space-time codes are provided.

Abstract: An adaptive receiver for multiple access communication, illustratively UWB multiple access communication, is provided. One embodiment of a detector is derived based on the finding that an symmetric alpha-stable model is more suitable for modeling the MAI in multiuser UWB systems than existing models. A myriad filter detector works better than all the known receiver structures proposed for statistical MAI cancellation. An intuitive expression for the tuning parameter K is provided which worked well in the examples considered.

Abstract: Novel non-data-aided maximum likelihood estimators for the delays and the attenuations in an ultra-wide bandwidth channel are proposed. Numerical results show that these new estimators outperform the previous non-data-aided maximum likelihood channel estimators derived in the literature. Moreover, in some cases, the performances of the new non-data-aided estimators approach those of the data-aided estimators, enabling us to reduce the overhead expense of pilot symbols.

Abstract: Pilot symbol assisted modulation (PSAM) techniques for Rayleigh and Rician fading channels are derived. Previous techniques implement PSAM signal detectors as an ad-hoc design, using pilot symbols to first estimate channel gain, and then using channel gain estimates in a conventional coherent detector to make data decisions. Although this structure may be effective for binary phase shift keying in Rayleigh fading, it is suboptimal for Rician fading and for 16-ary quadrature amplitude modulation in Rayleigh fading. According to techniques disclosed herein, a PSAM signal detector jointly processes pilot symbols and data symbols. The performance of signal detectors according to embodiments of the invention is analyzed and compared with that of conventional detectors. Numerical results are presented to show that the performance gain of a proposed new PSAM signal detector over conventional PSAM detectors can be as much as 2 or 3 dB for Rician fading in some cases.

Abstract: Two novel receiver structures which surpass the performance of the conventional matched filter receiver are proposed for ultra-wide bandwidth multiple access communications. The proposed receiver structures are derived based on a more appropriate statistical model for the multiple access interference than the generally used Gaussian approximation.

Abstract: New systems and methods are provided which use a new pulse shape which performs better in certain circumstances than the raised cosine pulse.