4,828 research outputs found
Preamble design using embedded signalling for OFDM broadcast systems based on reduced-complexity distance detection
The second generation digital terrestrial television broadcasting standard (DVB-T2) adopts the so-called P1 symbol as the preamble for initial synchronization. The P1 symbol also carries a number of basic transmission parameters, including the fast Fourier transform size and the single-input/single-output as well as multiple-input/single-output mode, in order to appropriately configure the receiver for carrying out the subsequent processing. In this contribution, an improved preamble design is proposed, where a pair of training sequences is inserted in the frequency domain and their distance is used for transmission parameter signalling. At the receiver, only a low-complexity correlator is required for the detection of the signalling. Both the coarse carrier frequency offset and the signalling can be simultaneously estimated by detecting the above-mentioned correlation. Compared to the standardised P1 symbol, the proposed preamble design significantly reduces the complexity of the receiver while retaining high robustness in frequency-selective fading channels. Furthermore, we demonstrate that the proposed preamble design achieves a better signalling performance than the standardised P1 symbol, despite reducing the numbers of multiplications and additions by about 40% and 20%, respectively
Asymptotically optimal cooperative wireless networks with reduced signaling complexity
This paper considers an orthogonal amplify-and-forward (OAF) protocol for cooperative relay communication over Rayleigh-fading channels in which the intermediate relays are permitted to linearly transform the received signal and where the source and relays transmit for equal time durations. The diversity-multiplexing gain (D-MG) tradeoff of the equivalent space-time channel associated to this protocol is determined and a cyclic-division-algebra-based D-MG optimal code constructed. The transmission or signaling alphabet of this code is the union of the QAM constellation and a rotated version of QAM. The size of this signaling alphabet is small in comparison with prior D-MG optimal constructions in the literature and is independent of the number of participating nodes in the network
Space-Time Trellis and Space-Time Block Coding Versus Adaptive Modulation and Coding Aided OFDM for Wideband Channels
Abstract—The achievable performance of channel coded spacetime trellis (STT) codes and space-time block (STB) codes transmitted over wideband channels is studied in the context of schemes having an effective throughput of 2 bits/symbol (BPS) and 3 BPS. At high implementational complexities, the best performance was typically provided by Alamouti’s unity-rate G2 code in both the 2-BPS and 3-BPS scenarios. However, if a low complexity implementation is sought, the 3-BPS 8PSK space-time trellis code outperfoms the G2 code. The G2 space-time block code is also combined with symbol-by-symbol adaptive orthogonal frequency division multiplex (AOFDM) modems and turbo convolutional channel codecs for enhancing the system’s performance. It was concluded that upon exploiting the diversity effect of the G2 space-time block code, the channel-induced fading effects are mitigated, and therefore, the benefits of adaptive modulation erode. In other words, once the time- and frequency-domain fades of the wideband channel have been counteracted by the diversity-aided G2 code, the benefits of adaptive modulation erode, and hence, it is sufficient to employ fixed-mode modems. Therefore, the low-complexity approach of mitigating the effects of fading can be viewed as employing a single-transmitter, single-receiver-based AOFDM modem. By contrast, it is sufficient to employ fixed-mode OFDM modems when the added complexity of a two-transmitter G2 scheme is affordable
The Noncoherent Rician Fading Channel -- Part I : Structure of the Capacity-Achieving Input
Transmission of information over a discrete-time memoryless Rician fading
channel is considered where neither the receiver nor the transmitter knows the
fading coefficients. First the structure of the capacity-achieving input
signals is investigated when the input is constrained to have limited
peakedness by imposing either a fourth moment or a peak constraint. When the
input is subject to second and fourth moment limitations, it is shown that the
capacity-achieving input amplitude distribution is discrete with a finite
number of mass points in the low-power regime. A similar discrete structure for
the optimal amplitude is proven over the entire SNR range when there is only a
peak power constraint. The Rician fading with phase-noise channel model, where
there is phase uncertainty in the specular component, is analyzed. For this
model it is shown that, with only an average power constraint, the
capacity-achieving input amplitude is discrete with a finite number of levels.
For the classical average power limited Rician fading channel, it is proven
that the optimal input amplitude distribution has bounded support.Comment: To appear in the IEEE Transactions on Wireless Communication
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