Image transmission through UWB communication based on compressed sensing

1.1 Impulse Radio (IR) Ultra Wideband (UWB) Communications Ultra wideband (UWB) communication is a fast emerging technology that offers new opportunities such as high data rates, low equipment cost, low power, precise positioning capability and extremely low interference Ghawami (2005). A wide range of possible UWB communication system applications includes radars due to UWB ultra high precision ranging at the centimeter level, wireless personal area networks (WPAN), sensor networks, imaging systems, UWB positioning systems, etc. Yang (2004), Kshetrimayum (2009). From a commercial point of view, the high data rates are the most attractive feature of UWB systems for which speeds of over 100Mb/s have been demonstrated Ghawami (2005). There exist three main types of UWB technologies: impulse radio (IR UWB), direct sequence (DS UWB), and multi-band orthogonal frequency division multiplexing (MB OFDM) Ran (2009). IR UWB communication technique is essentially different from all other communication techniques because it is carrier free and uses for communication between transmitters and receivers very narrow radio frequency (RF) pulses generated from the UWB pulse generator, while traditional transmission systems transmit information by varying the power, frequency, and/or phase of a sinusoidal wave in a modulation process Kshetrimayum (2009), Yao (2007). Consequently, complicated frequency mixers and local oscillators for carrier frequency up and down conversion are not necessary Yao (2007). IR UWB modulation techniques are especially important because the UWB spectrum has been made available by the Federal Communication Commission (FCC) and it can be used with IRs developed to date Lin (2005). Waveforms for IR UWB are designed to obtain a flat frequency response over the bandwidth of the pulse and to avoid a DC component. The large spectrum of a UWB signal may interfere with existing users. In order to keep this interference to the minimum, FCC specifies spectral masks for different applications, i.e. the allowed power output for specific frequencies Ghawami (2005). A contiguous bandwidth of 7.5GHz is available in the frequency interval of (3.1− 10.6)GHz at a maximum power output of −41.3dBm/MHz which is considered as extremely low Ghawami (2005). The power spectral density (PSD) of UWB systems defined as a ratio of the transmitted power P in watts and a signal bandwidth B in hertz is extremely low as compared to other communication systems due to the very wide bandwidth B of short pulses that are typically of nanosecond or picosecond order Ghawami (2005). The selection of the impulse signal type for IR UWB communication system is essential since it determines

One of the scarcest resources in the wireless communication system is the limited frequency spectrum. Many wireless communication systems are hindered by the bandwidth limitation and are not able to provide high speed communication. However, Ultra-wideband (UWB) communication promises a high speed communication because of its very wide bandwidth of 7.5GHz (3.1GHz-10.6GHz). The unprecedented bandwidth promises many advantages for the 21st century wireless communication system. However, UWB has many hardware challenges, such as a very high speed sampling rate requirement for analog to digital conversion, channel estimation, and implementation challenges. In this thesis, a new method is proposed using compressed sensing (CS), a mathematical concept of sub-Nyquist rate sampling, to reduce the hardware complexity of the system. The method takes advantage of the unique signal structure of the UWB symbol. Also, a new digital implementation method for CS based UWB is proposed. Lastly, a comparative study is done of the CS-UWB hardware implementation methods. Simulation results show that the application of compressed sensing using the proposed method significantly reduces the number of hardware complexity compared to the conventional method of using compressed sensing based UWB receiver.

Recently, ultra wideband (UWB) communications have received increasing interest due to the high data rate achievable in a short distance. UWB communications can have strong interference mitigation capability. A multicarrier ultra wideband (MC-UWB) system has been introduced in (A.H. Tewfik, et al., (2002)) and (E. Saberinia, et al., (2002)). In the MC-UWB communication systems, multiple symbols are transmitted over different carriers simultaneously. The same symbol is retransmitted over different frequency bands by utilizing frequency hopping (FH) techniques. Frequency hopping and multicarrier technologies smooth the average power spectrum density of the system. In this paper, the expression of the power spectrum density of the MC-UWB system is derived. The radiated emission power for UWB communication systems is limited by the spectrum mask specified by wireless communication authorities, such as the federal communications commission (FCC) in United States. Different parameters in the MC-UWB system will have different effects on the power spectrum density and the maximal achievable data rate. The analysis of impact of parameters in the system on the power spectrum density will help the system designer select proper parameter set to fit in emission power regulation and the required data rate in practical UWB systems. Some examples of parameter selection are also given to illustrate the impact of different parameters in the system on the power spectrum density.

A digital pre-coding based serial compressed sensing (CS) ultra-wideband (UWB) communication system is proposed. By establishing a mathematical model, signal detection is studied based on the CS theory. Simulation results in the IEEE 802.15.3a channel model show that with a low sampling rate, the proposed system can operate in a regime of heavy intersymbol interference.

Compressive Sensing (CS) is a new sensing modality, which compresses the signal being acquired at the time of sensing. Signals can have sparse or compressible representation either in original domain or in some transform domain. Relying on the sparsity of the signals, CS allows us to sample the signal at a rate much below the Nyquist sampling rate. Also, the varied reconstruction algorithms of CS can faithfully reconstruct the original signal back from fewer compressive measurements. This fact has stimulated research interest toward the use of CS in several fields, such as magnetic resonance imaging, high-speed video acquisition, and ultrawideband communication. This paper reviews the basic theoretical concepts underlying CS. To bridge the gap between theory and practicality of CS, different CS acquisition strategies and reconstruction approaches are elaborated systematically in this paper. The major application areas where CS is currently being used are reviewed here. This paper also highlights some of the challenges and research directions in this field.

Ultrawideband (UWB) is a promising technology for getting high data rate communications. UWB communications refer to the utilization of signals with a frequency range (3.1 to 10.6 GHz) on the condition of having a fractional bandwidth of 20% or absolute bandwidth of 500 MHz or higher. The limited power spectral density of − 41.3 dBm/MHz allows UWB communications to be safely deployed with existing wireless communication systems without causing any interference. Consequently, UWB communication systems have been proposed for different outdoor and indoor scenarios. A variety of applications are suitable for UWB communications ranging from infostations, wireless sensor networks (WSNs), on-body communications, in addition to consumer, medical and military applications. Recently, this technology shows a promising step for indoor positioning accuracy where the functioning of navigation systems such as Global Positioning System (GPS) or GLObal NAvigation Satellite System (GLONASS) might be degraded. In this paper, the fundamental properties of UWB communications are presented with an illustration on the present and future direction of this technology.

Purpose – The purpose of this paper is to present a compressed sensing (CS)-based sampling system for ultra-wide-band (UWB) signal. By exploiting the sparsity of signal, this new sampling system can sub-Nyquist sample a multiband UWB signal, whose unknown frequency support occupies only a small portion of a wide spectrum. Design/methodology/approach – A random Rademacher sequence is used to sense the signal in the frequency domain, and a matrix constructed by Hadamard basis is used to compress the signal. The probability of reconstruction is proved mathematically, and the reconstruction matrix is developed in the frequency domain. Findings – Simulation results indicate that, with an ultra-low sampling rate, the proposed system can capture and reconstruct sparse multiband UWB signals with high probability. For sparse multiband UWB signals, the proposed system has potential to break through the Shannon theorem. Originality/value – Different from the traditional sub-Nyquist techniques, the proposed sampling system not only breaks through the limitation of Shannon theorem but also avoids the barrier of input bandwidth of analog-to-digital converters (ADCs).

This paper investigates spectrum shaping in ultrawideband (UWB) communications in order to introduce spectral nulls to limit interference with narrowband signals. Each transmitted symbol is represented by a monocycle "coded" Gaussian pulse, where use of the monocycle Gaussian pulse ensures that the UWB spectrum mask established by the Federal Communications Commission (FCC) is met and where the codeword is designed to generate a spectral null at the frequency or frequencies being used by existing narrowband devices. Signals obtained with different spectrum shapings (e.g., Butterworth, Chebyshev, elliptical) and by introducing nulls at multiple interference frequency bands are discussed. The performance of a monocycle coded UWB system with a spectral null in the presence of narroband interference (NBI) using single carrier block transmission with frequency domain equalization (SC-FDE) is simulated and compared with that of an uncoded SC-FDE UWB system using a single Gaussian monocycle. Our results show that NBI can be effectively suppressed by transmitting and matched filtering the pulse with a spectral null at the interference frequency, therefore improving the robustness of SC-FDE UWB to NBI.

A software-defined radio (SDR) for ultrawideband (UWB) communication systems places several stringent requirements on the analog-to-digital converter (ADC). One alternative to using a single ADC is to sample the received signal with an array of lower speed ADCs that were driven by interleaved sampling clocks; however, mismatches among the ADCs will result in signal distortion. This paper makes three important contributions to overcoming this problem: 1) analytical quantification of the impact of ADC gain, offset, and timing mismatches on the performance of a time-interleaved sampling ADC array for UWB signals; 2) demonstration of the efficacy of using a pilot-based matched-filter architecture to mitigate the impact of timing mismatches in the presence of multipath; and 3) implementation of an 8-ADC time-interleaved UWB SDR testbed that operates at an effective sampling frequency of 6.4 GHz. In addition, our findings allow for the design specification of the number of pilots required to obtain a desired system performance. The simulation and measured performance results from this paper demonstrate that ADC mismatches can be controlled to within plusmn10%, yielding acceptable levels of distortion and bit-error-rate (BER) performance on the UWB SDR testbed. Both analytical and simulation results also demonstrate the efficacy of a pilot-based matched filter in mitigating the impact of timing mismatch errors, even in the presence of multipath.

Transmitted reference (TR) systems have recently been proposed for ultra wideband (UWB) communications. They considerably simplify synchronization and channel estimation, which are known to be difficult problems in UWB communications. We extend existing receivers for TR-UWB systems by replacing the correlation operation by a linear combination of specific parts of the correlation and weighting the parts that have a small noise contribution more than parts that have a large noise contribution. This turns out to improve the performance considerably.

We propose a time division multiple access (TDMA) scheme for the BPSK modulated single carrier block transmission with frequency domain equalization (SC-FDE) over ultra-wideband (UWB) communications. The transmitter and receiver matrices for the proposed TDMA SC-FDE system are derived to achieve the multiple access interference (MAI) free and interblock-interference (IBI) free transmission without the insertion of cyclic prefix (CP) between blocks, circumventing the need for long CP and large FFT size in high speed UWB communications. The performance of the proposed TDMA SC-FDE system over UWB channels is investigated and compared with that of the block spread code division multiple access (CDMA) scheme. The effects of oversampling diversity and imperfect channel estimation are also investigated. Results show that the proposed TDMA scheme can effectively eliminate the error floor in CDMA due to insufficient CP, and it is more efficient to accommodate larger number of users than CDMA in high data rate transmission

Ultra-WideBand (UWB) communication systems are usually classified as any communication system whose instantaneous bandwidth is many times greater than the minimum bandwidth required to deliver information. UWB communication is fundamentally different from all other communication techniques because it employs extremely narrow Radio Frequency (RF) pulses to communicate between transmitters and receivers. Utilizing short-duration pulses as the building blocks for communications directly generates a very wide bandwidth and offers several advantages, such as large throughput, covertness, robustness to jamming, and coexistence with current radio services. UWB technology offers a promising solution to the RF spectrum drought by allowing new services to coexist with current radio systems with minimal or no interference. This coexistence brings the advantage of avoiding the expensive spectrum licensing fees that providers of all other radio services must pay. In this chapter, the application of UWB technology in military areas has been summarized. Its wider applications has been evaluated over several leading technology including military technology systems, government sectors, communication systems, surveillance systems, rescuing, logistics entertainment, public transport, and others.

The emerging compressive sampling (CS) theory makes processing ultra-wide-band (UWB) signal at a low sampling rate possible if the underlying signal has a sparse representation in a certain basis. The feasibility of model based compressive sampling for ultra-wide-band (UWB) signal is investigated. In this paper, a multichannel compressive sampling architecture is developed to capture UWB signal at a rate much lower than Nyquist rate. The proposed framework considers sub-Nyquist sampling stream of delayed and weighted versions of a known signal with finite support in time domain. A basis function is constructed to realize sparse signal representation. To reduce the hardware cost, a segmented architecture is suggested. In addition, a joint signal recovery algorithm is presented. Experimental results indicate that, with this system, a UWB signal sampled at about 4% of Nyquist rate still can be recovered with overwhelming probability.

Multiple-symbol differential detection (MSDD) is a promising technique to enhance the performance of ultra-wideband (UWB) communications without estimating the channel explicitly. In this context, the generalized log-likelihood ratio test (GLRT) for MSDD was developed, and the hard-output multiple-symbol detector was proposed, which exhibits considerable bit-error-rate (BER) performance improvement over transmitted reference transmissions. In this paper, we further improve the system performance by incorporating error correction code (ECC) and iterative processing at the receiver. The soft-input soft-output (SISO) MSDD is developed to deliver a posteriori information to the outer ECC decoder and enables iterative detection and decoding. Simulations show that the iterative processing achieves significant gains over the existing MSDD in UWB communications.

Compressed sensing or compressed sampling (CS) has been receiving a lot of interest as a promising method for sparse signal recovery from fewer sensors, while the complexity is not high. Because of the sparsity of the Ultra-Wideband (UWB) channel, CS has been used to the UWB channel estimation to reduce demands and complexity of high-speed analog-to-digital (A/D) converters. In this paper, pre-filtering method for UWB channel estimation based on the theory of CS is developed. An FIR filter is adopted at the transmitter, so that we get a measurement matrix, a quasi-Toeplitz matrix, leading to a better reconstruction accuracy of CS. Furthermore, there is no need to add a measurement matrix element in the receiver, which magnifies the noise in the UWB channel. That also makes the receiver simplified. Extensive simulations show that the proposed approach can successfully suppress the additive white Gaussian noise (AWGN). Finally, when the UWB channel estimation method we proposed is used in the correlation detection of UWB signals, it develops better performance of the bit error rate (BER) at lower sampling rate.