Energy efficient binary PPM/code-multiplexed transmitted-reference multi-user UWB system

This paper considers the influence of multi-user interference (MUI) on an impulse radio ultra-wideband (UWB) communication system. Binary pulse position modulation is employed with time hopping (TH) for multiple access communications. The users are assumed to transmit asynchronously. A technique to reduce the MUI is presented. It is shown that this approach is effective for UWB systems in both additive white Gaussian noise (AWGN) and IEEE 802.15.3a channels.

Narrow-band interference (NBI) from the coexisting narrow-band services affects the performance of ultra wideband (UWB) systems considerably due to the high power of these narrow-band signals with respect to the UWB signals. Specifically, IEEE 802.11a systems which operate around 5 GHz and overlap the band of UWB signals may interfere with UWB systems significantly. In this paper, we suggest a novel NBI suppression technique based on singular value decomposition (SVD) algorithm in time hopping UWB (TH-UWB) systems. SVD is used to approximate the interference which then is subtracted from the received signals. The algorithm precision and closed-form bit error rate (BER) expression are derived in the wireless multipath channel. Comparing with the conventional suppression methods such as a notch filter and a RAKE receiver, the proposed method is simple and robust and especially suitable for UWB systems.

This paper studies the effects of multiple access interference (MAI) for ultra wideband (UWB) systems in AWGN and multipath fading channels. Time hopping (TH) and direct sequence (DS) based UWB spreading approaches are performed, utilizing binary pulse amplitude modulation (PAM) and pulse shape modulation (PSM). Both the possibilities of having synchronous and asynchronous users have been taken into account. In the fading channel case, different coherent and non-coherent detection methods have been considered. Simulated performance results are depicted for the above mentioned UWB systems when a variable number of equally powered users are operating in the channel. Results show that in both the AWGN and fading channel the DS system performance shows sensibly different results in the synchronous and asynchronous case. This is due to the continuous time transmission of the different users. This problem does not occur in systems using TH spreading since the different users are less overlapped in time, due to the spreading approach used. In the fading channel, TH systems show a general higher performance loss in all cases compared to DS, in contrast to what happens in the AWGN case. That is, the allocation of the TH codes creates a higher interfering effect due to MAI in the presence of multipath fading. In general, DS-based systems outperform the corresponding TH ones.

In this paper, multiple receive antennas are applied to multi-user binary pulse amplitude modulation (2PAM) time hopping (TH) ultra-wideband (UWB) systems to achieve high-data-rate communications. The effects of spatial diversity on the performance of 2PAM-TH-UWB systems are analytically investigated. We derive the expression for the received SINR after spatially combining and evaluate the bit error rate (BER) performance. Numerical results show that the BER performance can be enhanced by spatial diversity combining.

Multiuser detection of time-hopping PPM UWB system in the presence of multipath fading

The recently approved IEEE 802.15.4a standard defines an ultra-wideband (UWB) based physical layer using concatenated coding with mixed binary phase-shift keying and binary pulse-position modulation (BPSK-BPPM) and direct-sequence spreading with time hopping. The concatenated code consists of an outer Reed-Solomon (RS) and an inner convolutional code, and the coding and modulation are combined such that both coherent and noncoherent receiver architectures are supported. In this paper, the error-rate performance of IEEE 802.15.4a compliant UWB radios is investigated. To this end, semi-analytical expressions for the bit-error rate (BER) and frame-error rate (FER) of the coded UWB system are derived. The presented framework is comprehensive in that (i) different methods for generating reliability information (i.e., decoding metrics), (ii) the effects of suboptimal multipath combining, and (iii) coherent and noncoherent reception methods are included. Furthermore, a particularly suited errors-and-erasures RS decoding scheme is devised. The evaluation of the error-rate expressions together with simulation results for realistic UWB channels show that (i) the error-rate approximations are tight over wide ranges of BER and FER, (ii) symbol-wise metrics are clearly advantageous over bit-wise metrics for decoding of the convolutional code, (iii) combining the 5 to 10 strongest multipath components approaches the performance of full combining within 1-2 dB for residential and 3-5 dB for outdoor UWB environments, and (iv) the simplicity of noncoherent detection comes at loss of more than 10 dB in signal-to-noise ratio compared to coherent detection.

This paper studies the performance differences of three low data rate ultra wideband (UWB) systems in interfered AWGN and multipath channels. The studied systems are based on ultra wideband frequency modulation (UWB-FM), direct sequence UWB (DS-UWB) and multiband orthogonal frequency division multiplexing (MB-OFDM). The systems are studied in very high and ultra high frequency bands (VHF/UHF), i.e. 230 - 390 MHz, and 6.336 - 7.920 GHz. The VHF/UHF channel model is based on the measurements carried out in typical Finnish forest, whereas channel model for 6.336 - 7.920 GHz band is based on the modified Saleh-Valenzuela model. The intentional interference locates at the centre of the studied band having a 20 MHz bandwidth. In the literature, the comparison of the different low data rate UWB systems is rather insignificant. Therefore, the results of this paper are filling up this evident gap. The same spectral allocation and data rate are used as a starting point for a study. In the lower band, DS-UWB seems to tolerate more interference than UWB-FM in AWGN and multipath channels. The interference power can be higher for UWB-FM than MB-OFDM without performance degradation in AWGN channel in the upper band. The system performance starts to decrease with the same interference power in the case of MB- OFDM and UWB-FM in the interfered multipath channels in the upper band.

In previous works, the performance of DS-UWB (Direct Sequence- Ultra Wide Band) systems in a multiuser scenario with binary pulse amplitude modulation has been studied. In most of these works, independent identically distributed (i.i.d) random sequences have been considered and no optimization of the DS-UWB performance with respect to the choice of spreading sequences has been done. In this paper, we investigate an analysis of multi-user interference (MUI) term in three different families of traditional spreading sequences; i.i.d, Gold and Kasami sequences on Rayleigh and AWGN (additive white gaussian noise) channel. Then, we evaluate the bit error rate (BER) performance of conventional receiver on both channels to confirm the results found about MUI.

By dividing the available spectrum into multiple bands, multi-band ultra-wideband (UWB) systems possess many advantages, such as the flexibility to eliminate possible interference and coexistence problems with available wireless standards. UWB channels have large delay spread, causing inter- symbol interference (ISI) in high rate systems. The RAKE receiver is often used to capture multipath energy, but it is incapable of ISI compensation, causing severe bit error rate (BER) degradation in practical UWB channels. This paper proposes an over-sampling multi-channel equalizer per sub-band for multi-band UWB. The performance of the proposed receiver is compared with the RAKE receiver through analytical and simulation studies. The proposed equalizer has been shown to be able to handle ISI under any channel conditions or data rate presented, with an acceptable BER. In addition, the rich multipath diversity of the UWB channels is harnessed by the over-sampling scheme, for output SNR improvement. one. Therefore, equalization receiver based on adaptive algorithms seems to be an effective way to recover the transmitted data. With this consideration, we propose an over-sampling multi-channel equalizer per sub-band for a multi-band UWB system, which provides more effective inter-symbol interference (ISI) suppression compared with the conventional RAKE receiver when operating in channels with large delay spread. Through detailed theoretical analysis and extensive simulations, we are able to show that the proposed 4-arm equalizer scheme is superior to a 4-arm conventional RAKE receiver in the presence of ISI at all signal-to-noise ratios (SNRs). Based on the method presented in (4), the simulated performance is shown to conform to analytical predictions. The RAKE receiver is incapable of ISI compensation, and a moderate level of ISI is shown to cause severe bit error rate (BER) degradation. The proposed over-sampling equalizer, on the other hand, is able to handle ISI under any channel conditions or data rate, with an acceptable BER. Over- sampling is shown to be able to achieve diversity gain, and improves the output SNR.

Duobinary partial response (PR) filtered single-carrier frequency-domain multi-access (SC-FDMA) uplink has a potential to achieve higher spectral efficiency (SE) by allowing spectrum overlapping between adjacent users. However, strong multiuser interference (MUI) degrades the bit-error rate (BER) and throughput performances. In this paper, we present two types of frequency-domain MUI cancellation technique for duobinary PR filtered SC-FDMA, which are frequency-domain iterative parallel MUI cancellation (FD-IPMUIC) and frequency-domain iterative successive MUIC (FD-ISMUIC). A series of minimum mean-square error based frequency-domain equalization (MMSE-FDE), FD-MUIC, and soft-decision decoding using soft output Viterbi algorithm (SOVA) is repeated for a sufficient number of times. By using the SOVA, MMSE-FDE weight and MUI replica are updated. Computer simulation results show that both the BER performance and SE can be improved.

When several ultra-wide band (UWB) communication systems coexist, multiuser interferences (MUI) are unavoidable. To cope with the MUI of UWB systems, the independent of UWB signals are investigated and a novel receiving method is proposed. At first several antennas are utilized to receive the transmitted signals of different UWB users, and the mixture signals are gained. Then the mixed signals are separated by independent component analysis algorithm to recover the transmitted signals of each UWB users. Finally, the information of each UWB users transmitted is demodulated. Computer simulations show that the proposed method can efficiently resist the interference of different UWB users.

The emerging trends of wireless communication and ever growing demand of very high data rate from users created the need for new technologies that could satisfy this need under limited bandwidth. A 60-GHz Ultra-Wideband (UWB) system that can support up to 7 Gbps data rate, which is 10 times faster than the data rate of the Wi-Fi 802.11n, is one of the promising options. The system utilizes higher order modulation and advanced coding schemes known as Adaptive Modulation and Coding (AMC). However, inappropriate selection of modulation level and coding rate can lead to low data rate particularly in the presence of Radio Frequency interference and multipath fading. Moreover, further performance degradation occurs when non-optimal decoder due to code constraint length was selected. This paper proposes and evaluates a duplex 60-GHz UWB system employing Orthogonal Frequency Division Multiplexing (OFDM-UWB) to boost the data rate and extend the coverage. Firstly, an OFDM-UWB system employing high order modulation that transmits data simultaneously over multiple carriers spaced apart at precise frequencies been simulated and validated using Matlab. Secondly, the system performance been analyzed when convolutional coding been introduced in term of Bit Error Rate (BER). The simulation results show that the BER performance of 16QAM is worse, with 6 dB penalties at BER of 10−3, compared with that of QPSK. Moreover, simulation also shows that there are 2 dB difference between the performance of R=1/2 and R=7/8, while the highest throughput been achieved when the 3/4 code rate is employed.

In this paper, we provide performance analysis for direct-sequence multiple-access ultra-wideband (UWB) systems operating in multipath environments when the effect of overlap between received pulses is included. Pulse overlap occurs when the pulse width is larger than the fine delay resolution of the UWB channel and is particularly important to consider in multidimensional pulse modulations. A closed-form bit error rate expression is derived and compared with simulations that employ UWB signals complying with the FCC UWB indoor emission mask and the channel model recommended by IEEE 802.15.3a. The detailed theoretical analysis and simulations reveal that channel-induced pulse overlap has a significant impact on UWB system performance. The results also show that compared with binary modulations, multidimensional biorthogonal pulse keying can improve power efficiency for multiple-access UWB systems under multipath fading, thereby providing an advantage for power-limited UWB communications.

This paper discusses ultra wideband (UWB) system performance in additive white Gaussian noise (AWGN) channel in the presence of partial band interference, whose special case is tone interference. In UWB case, most of the interference can be seen as partial band interference due to the extremely large inherent bandwidth of the desired signal. The given redefined formulas are verified with the corresponding simulation results. Study has focused on direct sequence (DS) based UWB system that uses binary pulse amplitude modulation (HPAM) as a data modulation scheme. DS-UWB is selected due to its better performance when related to the corresponding time hopping system in the interfered environment. Interference is assumed to be band limited and Gaussian distributed, and the presented analysis allows freely spacing and arbitrary bandwidth for the interfering signal. It has been proved that the general bit-error-rate (BER) formulas for wideband systems can be applied also to UWB with some modifications to calculate the upper bound for the UWB performance. The given approaches are very simple and can benefit the real system parameters for the desired link.

To solve the coexistence of ultra wideband (UWB) system with other existed narrowband systems operating within the UWB bandwidth, we propose an adaptive non-linear chirp UWB waveform based on the atan function in this paper. With the utilization of cognitive radio (CR) technology and the good time-frequency relationship of the chirp function, the flexible multiple narrowband interferences (NBIs) suppression can be achieved. Simulation results demonstrate the superior multiple NBIs suppression ability of the proposed scheme in direct sequence bipolar pulse amplitude modulation (DS-BPAM) UWB system, which is also compared with the linear chirp pulse based UWB system.