Multiband Ultra Wideband System Research Articles

A highly sustainable multi-band orthogonal wavelet code division multiplexing UWB communication system for underground mine channel

The underground mine channel is highly hostile for communication. A sustainable communication system is required to be integrated as a multipurpose system capable of transferring all types of information such as data, voice and video on identical infrastructure. With its large bandwidth, the Ultra Wide Band (UWB) provides a promising solution to satisfy these requirements. The Multi-Band Orthogonal Frequency Division Multiplexing (MBOFDM) UWB system provides high resilience to Inter-Symbol Interference (ISI) caused by multipath fading channels. This study compares the performance of various existing multi-band UWB systems in the IEEE UWB channel and underground mine channel: MBOFDM, Multi-Band Orthogonal Frequency Code Division Multiplexing (MBOFCDM) and Multi-Band Orthogonal Wavelet Division Multiplexing (MBOWDM). Further, the application of 2D spreading to the MBOWDM UWB system is attempted, and as a result, the Multi-Band Orthogonal Wavelet Code Division Multiplexing (MBOWCDM) UWB system is proposed. The performance of the MBOWCDM system in the IEEE UWB channel and underground mine channel is investigated. The performance of the MBOWCDM UWB system is observed to be superior to those of other multi-band UWB systems. Moreover, the MBOWCDM UWB system supports a higher data rate with low complexity and lower overheads.

Preamble-based improved channel estimation for multiband UWB system in presence of interferences

Interferences reduce the performance of a correct data signal detection and decoding. This problem becomes severe when interferences exist during the period of channel estimation. This will destroy the accuracy of channel estimation and will eventually result severe degradation in the performance of signal detection and decoding in the entire data packet/frame. In this article, we propose an improved channel estimation technique for multiband orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) system in presence of interferences. In particular, we work towards a preamble-based channel estimation technique in multi-access and narrowband interfering environments. We construct two preamble symbols with opposite, both in amplitude and phase, sequences in frequency-domain. Time-domain redundancy (TR) is introduced into these preamble symbols before transmission. Based on this time-domain redundancy property, we eliminate multi-access interference (MAI) through an adaptive select and replace (ASR) scheme. We show that the use of opposite sequences in preambles leads a simple addition, subtraction and compare (ASC) scheme to cancel narrowband interference (NBI). In addition, we apply a frequency-domain filter, driven by channel's power delay profile (PDP), to get a further enhancement in the estimation accuracy. Simulation results urge that our proposed technique outperforms the conventional channel estimation methods.

Error Analysis of Hybrid DS-Multiband-UWB Multiple Access System in the Presence of Narrowband Interference

This paper proposes a hybrid multiband (MB) ultra wideband (UWB) system with direct sequence (DS) spreading. The theoretical error analysis for the DS-MB-UWB multiple access system with Rake receiver in the presence of multipath and narrowband interference is developed. The developed theoretical framework models the multiple access interference (MAI), multipath interference (MI) and narrowband interference for the designed UWB system. It is shown that the system error performance corresponding to the combining effects of these interference can be accurately modeled and calculated. Monte Carlo simulation results are provided to validate the accuracy of the model. Additionally, it is found that narrowband interference can be mitigated effectively in the multiband UWB system by suppressing the particular UWB sub-band co-existing with the interfering narrowband signal. A typical improvement of 5dB can be achieved with 75% sub-band power suppression. On the other hand, suppression of UWB sub-band is also found to decrease frequency diversity, thus facilitating the increase of MAI. In this paper, the developed model is utilized to determine the parameters that optimize the UWB system performance by minimizing the effective interference.

Performance Evaluation of a Multi-band UWB Location and Communication System Based on Modified Gegenbauer Functions

Ultra wide band (UWB) may offer very efficient solutions for various communication and sensing applications. Two approaches have emerged, which meet all the communication requirements: impulse and multi-band systems. The present work is concerned in the second approach. So, we propose to use orthogonal functions called Modified Gegenbauer Functions (MGF) in a multi-band UWB system occupying the 3---6 GHz frequency band. Different scenarios are studied and compared in the scope of a system offering communication and location capabilities for subway trains. In order to evaluate the performance of the proposed system, the bit error rate (BER) values for communication are calculated and analyzed in the presence of multi-user interference, assuming asynchonous users. It is shown that Gegenbauer functions offer the performance required for our multi-band UWB communication and location system.

Frequency Ambiguity Resolution for Multiband UWB Systems

A combination of orthogonal frequency division multiplexing (OFDM) with multiband frequency hopping (FH) is regarded as a promising solution for realizing ultra-wideband (UWB) systems. This paper deals with a modified maximum likelihood approach for frequency ambiguity resolution in the multiband UWB system. By using computer simulation, the synchronization performance of the traditional and proposed methods is evaluated in terms of probability of synchronization failure.

Power controlled channel allocation for multiuser multiband UWB systems

Emerging ultra-wideband (UWB) technology offers a great potential for the design of high-speed short-range communications. However, in order for a UWB device to coexist with other devices, the transmitted power level of UWB is strictly limited by the FCC spectral mask. Such limitation poses a significant design challenge to any UWB system. An efficient management of the limited power is thus a key feature to fully exploit the advantages of UWB. In this paper, a cross layer multiuser multiband UWB scheme is proposed to obtain the optimal subband and power allocation strategy. Optimization criteria involve minimization of power consumption under the constraints on the packet error rate, the data rate, and the FCC limit. To ensure the system feasibility in variable channel conditions, an algorithm to jointly manage the rate assignment of UWB devices, subband allocation, and power control is proposed. A computationally inexpensive suboptimal approach is also developed to reduce the complexity of the problem, which is found to be NP hard. Simulation results under UWB channel model specified in the IEEE 802.15.3a standard show that the proposed algorithm achieves comparable performances to those of the complex optimal full search approach, and it can save up to 61% of transmit power compared to the current multiband scheme in the standard proposal. Moreover, the proposed algorithm can obtain the feasible solutions adaptively when the initial system is not feasible for the rate requirements of the users.

Polarization diversity for multiband UWB systems

Ultra-wideband (UWB) transmission provides a fast local range wireless connection using the same frequency spectrum assigned to other narrowband communication standards. A precise knowledge of the indoor transmission channel is necessary to obtain high performance. Several channel models have been presented in the literature, but normally without considering the distortion effect caused by a real UWB antenna. A detailed antenna model shows that the radiation pattern varies with frequency, i.e., different receiver positions and antenna orientations result in different antenna frequency responses. In order to obtain a more uniform coverage over the indoor area, two transmitting antennas with orthogonal polarization can be used. The receiver can use a single antenna whose orientation and position is arbitrary within the coverage area, resulting in a special case of a 2:1 MISO system in which a space-time encoding is used at the transmitter. The target is to employ the polarization diversity to obtain a constant quality of symbol detection while the receiver moves around in the coverage area. The proposed polarization diversity scheme is applied in an UWB multiband scenario and it is compared to both a single antenna scheme and a classical space diversity scheme employing a single polarized antenna array.

A low clock frequency FFT core implementation for multiband full-rate ultra-wideband (UWB) receivers

This paper discusses the design, implementation and synthesis of an FFT module that has been specifically optimized for use in the OFDM based multiband UWB system, although the work is generally applicable to many other OFDM based receiver systems. Previous work has detailed the requirements for the receiver FFT module within the multiband UWB ODFM based system and this paper draws on those requirements coupled with modern digital architecture principles and low power design criteria to converge on our optimized solution particularly aimed at a low-clock rate implementation. The FFT design obtained in this paper is also applicable for implementation of the transmitter IFFT module therefore only needing one FFT module in the device for half-duplex operation. The results from this paper enable the baseband designers of the 200 Mbit/sec variant of multiband UWB systems (and indeed other OFDM based receivers) using system-on-chip (SoC), FPGA and ASIC technology to create cost effective and low power consumer electronics product solutions biased toward the very competitive market.

Numerical precision requirements on the multiband ultrawideband system for practical consumer electronic devices

This paper discusses the requirements on the numerical precision for a practical multiband ultra-wideband (UWB) consumer electronic solution. To this end, we first present the possibilities that UWB has to offer to the consumer electronics market and the possible range of devices. We then show the performance of a model of the UWB baseband system implemented using floating point precision. Then, by simulation we find the minimal numerical precision required to maintain floating-point performance for each of the specific data types and signals present in the UWB baseband. Finally, we present a full description of the numerical requirements for both the transmit and receive components of the UWB baseband. The numerical precision results obtained in this paper can then be used by baseband designers to implement cost effective UWB systems using system-on-chip (SoC), FPGA and ASIC technology solutions biased toward the competitive consumer electronics market.

Digital-carrier multi-band user codes for baseband UWB multiple access

The growing interest towards ultra-wideband (UWB) communications stems from its unique features such as baseband operation, ample multipath diversity, and the potential of enhanced user capacity. But since UWB has to overlay existing narrowband systems, multiple access has to be achieved in the presence of narrowband interference (NBI). However, existing baseband spreading codes for UWB multiple access are not flexible in handling NBI. In this paper, we introduce two novel spreading codes that not only enable baseband UWB multiple access, but also facilitate flexible NBI cancellation. We construct our codes using a single carrier or multiple carriers (SC or MC), which can be implemented with standard discrete-cosine transform (DCT) circuits. With our SC/MC codes, NBI can be avoided by simply nulling undesired digital carriers. Being digital, these SC/MC codes give rise to multi-band UWB systems, without invoking analog carriers. In addition, our SC/MC codes enable full multipath diversity, and maximum coding gains. Equally attractive is their capability to reduce the number of interfering users, with simple matched filter operations. Comprehensive simulations are also carried out to corroborate our analysis.