Jean-François Hélard

Data-aided channel estimation for turbo-PIC MIMO detectors

We consider data-aided channel estimation for multiple input multiple output (MIMO) systems when iterative parallel interference cancellation (PIC) is performed for signal detection. We compare some data-aided channel estimation methods based on expectation maximization (EM) algorithm or on hard estimated transmit symbols. In particular, we propose a modified EM-based approach and show that when few iterations are to be performed, it provides considerable performance improvement.

Should MIMO orthogonal space-time coding be preferred to non-orthogonal coding with iterative detection?

In order to propose practical solutions to the future communication systems employing MIMO structures, we compare the performances obtained by using orthogonal and non-orthogonal space-time codes. For the latter case, we propose to use a simple iterative detector based on parallel interference cancellation. The choice of an orthogonal or a non-orthogonal code with iterative detection is then studied for several space-time coding schemes and for two or three antennas at transmitter. We show that when frames are long enough so that we can estimate properly the detector parameters, non-orthogonal codes can provide considerable gain over orthogonal designs at the price of a more complex detector

Increase in multicast OFDM data rate in PLC network using adaptive LP-OFDM

Linear precoding (LP) technique applied to OFDM systems has already proved its ability to significantly increase the system throughput in a powerline communication (PLC) context. In this paper, we propose resource allocation algorithms based on the LP technique to increase the multicast OFDM systems bit rate. The conventional multicast capacity is limited by the user which experiences the worst channel conditions. To increase the multicast bit rate, these proposed algorithms assign subcarriers and bits to different multicast users. Simulations are run over PLC channels and it is shown that the proposed solutions offer a bit rate gain up to 37% compared to the conventional multicast bit rate.

Overlaid or time-multiplexed pilots for channel estimation in iterative MIMO receivers

We consider the use of overlaid pilots for multiple input multiple output (MIMO) channel estimation in the context of single-user and single-carrier modulation. Imposing no loss in spectral efficiency, overlaid pilots are potentially of special interest, notably in relatively fast fading channels. However, when channel is to be estimated over short sequences, estimation errors can be important, due to the non-zero cross-correlation of data and pilot sequences. We show how these estimation errors limit the performance of the receiver, when iterative data detection and channel estimation is performed. Also, for the case of iterative detection at receiver, we compare the performances of the overlaid and the time-multiplexed pilot schemes.

A Joint Channel and Carrier Frequency Offset Estimation Based on Spread Pilot for Future Broadcasting Systems

In this paper, we propose a novel and simple joint channel frequency response (CFR) and carrier frequency offset (CFO) estimation based on 2D spread pilots for digital video broadcasting (DVB) systems. The advantage of the proposed algorithm compared to DVB-T/H standard, is to estimate the CFR and the CFO using the same pilot symbols. The performance evaluated over a realistic channel model, in a mobility scenario, in the presence of CFO, shows the efficiency of this technique which turns out to be a promising joint CFR and CFO estimation technique for the future DVB systems.

Cross-Layer Resource Allocation for MB-OFDM UWB Systems

The demand of wireless services is increasing and new generations of mobile radio systems are promising to provide higher data rates and a large variety of applications to mobile users. Besides, one of the major challenging problems in future wireless communication systems is how to offer the ability to transport multimedia services at different channel conditions and bandwidth capacities with various quality of service (QoS) requirements. However, this goal must be achieved under the constraint of limited available frequency spectrum because numerous licensed services and applications already exploit the spectral resource up to several gigahertz. Thereby, the multiple access and the coexistence are challenging matters for the next generation wireless communication systems. Two exciting solutions have recently risen to circumvent the limited frequency spectrum problem. The first solution is based on spectrum sensing and dynamic spectrum access (DSA) techniques to find available spectrum which can be used by a cognitive radio user without causing any harmful interference to licensed users. The other solution is to set up underlay communications that would allow so-called secondary users to judiciously exploit some frequency resource already allocated to licensed primary users such that the former does not impact on the quality of the communications of the latter significantly. The latter solution can namely be achieved by imposing tough radiation restrictions to the secondary users. In that context, ultra-wideband (UWB) has recently been attracting great interest as a suitable technology for unlicensed short range communications. With the data rate of several hundred Mbps, and the restricted power transmission, UWB demonstrates great potential in the coexistence issue and the support of multimedia services such as highdefinition television (HDTV), videos and music sharing, console gaming, etc., in home networks known as the wireless personal area network (WPAN). Given the power constraint and the extremely wide bandwidth of UWB, a fundamental problem arises is how to manage the multiple-user access to efficiently utilize the bandwidth, support the QoS requirements of multimedia applications and provide fairness among the existing users. Moreover, to this date, research works on resource allocation for UWB communications are still limited. Based on the WiMedia Alliance, solution proposed for the UWB communications, the objective of this chapter is to define a new approach for the spectrum sharing and multiple access problems in the scope of the resource allocation in UWB systems while taking into account the various system constraints. Thus, to deal with

A new waveform based on linear precoded multicarrier modulation for future digital video broadcasting systems

Orthogonal Frequency Division Multiplexing (OFDM) has been perceived as one of the most effective transmission schemes for multipath propagation channels. It has been widely adopted in most of the digital video broadcasting (DVB) standards such as DVB-T in Europe, DMB-T in China, FLO in North America, ISDB-T in Japan. The major reason for this success lies in the capability of OFDM to split the single channel into multiple parallel intersymbol interference (ISI) free subchannels. It is easily carried out by implementing Inverse Fast Fourier Transform (IFFT) at the transmitter and Fast Fourier Transform (FFT) at the receiver [1]. Therefore, the distortion associated to each subchannel, also called subcarrier, can be easily compensated for by one coefficient equalization. For that purpose, the receiver needs to estimate the channel frequency response (CFR) for each subcarrier. In the DVB-T standard [2], one subcarrier over twelve is used as pilot for CFR estimation as illustrated in Fig. 1, i.e. symbols known by the receiver are transmitted on these subcarriers. Thus, the receiver is able to estimate the CFR on these pilot subcarriers and to obtain the CFR for any subcarrier using interpolating filtering techniques [3]. Nevertheless, OFDM systems are very sensitive to synchronization error such as carrier frequency offset (CFO) or sampling frequency offset (SFO) [4]. Indeed, when the carrier frequency or the sampling frequency of the transmitter and the receiver are not equal, the orthogonality between the different subcarriers is lost which can lead to strong intercarrier interference (ICI) effects [4]. This is why in addition to the scattered pilot subcarriers used for CFR estimation, continuous pilot subcarriers have been defined in the DVB-T standard [2] to estimate the CFO and the SFO [5]. Fig. 1 depicts the locations of the data subcarriers and the pilot subcarriers over the time and frequency grid as defined in the DVB-T standard. The originality of this work is to reduce the overhead part resulting from pilot insertion by using a joint CFR, CFO and SFO estimation approach based on a linear precoding function. Eventually, these pilots dramatically reduce the spectral efficiency and the useful bit rate of the system. The basic idea consists in using a two-dimensional (2D) linear Source: Digital Video, Book edited by: Floriano De Rango, ISBN 978-953-7619-70-1, pp. 500, February 2010, INTECH, Croatia, downloaded from SCIYO.COM

Innovative Space-Time-Space Block Code for Next Generation Handheld Systems

Broadcasting digital TV is currently an area of intensive development and standardisation activities. Actually, different groups are working on the standardisation problem. In Europe, the digital video broadcasting (DVB) consortium has adopted different standards for terrestrial (DVB-T) fixed reception, handheld (DVB-H) reception, satellite (DVB-S) reception as well as an hybrid reception like DVB-SH. In June 2008, the DVB-T2 was born extracting a lot of specifications from DVB-S2 and proposing some specifications for an eventual use of handheld reception. Now, we are working towards a second generation of DVB-SH called next generation handheld (NGH). Technically, DVB-SH system provides an efficient and flexible mean of carrying broadcast services over an hybrid satellite and terrestrial infrastructure operating at frequencies below 3 GHz to a variety of portable, mobile and fixed terminals. Target terminals include handheld, vehicle-mounted, nomadic (e.g. laptops) and stationary terminals. The broadcast services encompass streaming services such as television, radio programs as well as download services enabling for example personal video recorder services. Typically, Lbands (1-2 GHz) and S-bands (2-4 GHz) are used for land mobile satellite (LMS) services. The DVB-SH system coverage is obtained by combining a satellite component (SATC) and, where necessary, a terrestrial component (TC) to ensure service continuity in areas where the satellite alone cannot provide the required quality of service (QoS). The SATC ensures wide area coverage while the TC provides cellular-type coverage. In the DVB-SH standard, two main physical layer configurations are supported. SH-A allows (but does not impose) a single frequency network (SFN) (Mattson, 2005) between the SATC and the TC, using the orthogonal frequency division multiplexing (OFDM) technique. SH-B supports a time division multiplexing (TDM) for the SATC and the OFDM technique for the TC. The SFN presents great advantages by transmitting lower power at various sites throughout the coverage area. In an SFN, the different antennas transmit the same signal at the same moment on the same carrier frequency. The multi frequency network (MFN) allows however an optimization of the waveform and of the forward error correction (FEC) parameters according to the transmission environment. The existing SFN architectures are achieved in a single input single output system (SISO) since their deployment is very simple due to the use of one transmitting antenna by site. However, due to the increase of client services demand, it is desirable to deploy SFN with new multiple input multiple output (MIMO) techniques which ensure high spectrum efficiency as well as high diversity gain. In