This paper presents a novel memory optimization technique to exploit the analogy between correlation coefficients in MMSE-based channel estimators across multiple standards. The need for coefficient ...storage for robust MMSE channel estimators is expensive in terms of on-chip memory. Besides, the memory requirements grow linearly by integrating more standards onto one platform. Thus, it becomes inevitable to address the increased on-chip memory problem for such estimators. In this paper, we have shown that by exploiting the inherent similarities between LTE and DVB-H design parameters, a three-fold memory optimization may be achieved with minimal performance loss.
This paper investigates the performance of reduced- state trellis-based ISI equalizers, which are based on the so- called Ungerboeck and Forney observation models. Although the two models are ...equivalent when the Viterbi or BCJR equalizer is employed, their performances differ significantly when using reduced-complexity methods. It is demonstrated that practical equalizers operating on the Forney model outperform those operating on the Ungerboeck model for high signal-to-noise ratios (SNRs), while the situation is reversed for low SNR levels. A novel theoretical reduced-complexity equalization strategy that improves on previous Ungerboeck-based equalizers is proposed.
This work investigates linear precoding over non-singular linear channels with additive white Gaussian noise, with lattice-type inputs. The aim is to maximize the minimum distance of the received ...lattice points, where the precoder is subject to an energy constraint. It is shown that the optimal precoder only produces a finite number of different lattices, namely perfect lattices, at the receiver. The well-known densest lattice packings are instances of perfect lattices, however it is analytically shown that the densest lattices are not always the solution. This is a counter-intuitive result at first sight, since previous work in the area showed a tight connection between densest lattices and minimum distance. Since there are only finitely many different perfect lattices, they can theoretically be enumerated off-line. A new upper bound on the optimal minimum distance is derived, which significantly improves upon a previously reported bound. Based on this bound, we propose an enumeration algorithm that produces a finite codebook of optimal precoders.
Optimal lattices for MIMO precoding Kapetanovic, D.; Cheng, H. V.; Wai Ho Mow ...
2011 IEEE International Symposium on Information Theory Proceedings,
2011-July, 2011
Conference Proceeding
Consider the communication model y̅ = HF x̅ + n̅, where H; F are real-valued matrices, x̅ is a data vector drawn from some real-valued lattice (e.g. M-PAM), n̅ is additive white Gaussian noise and y̅ ...is the received vector. It is assumed that the transmitter and the receiver have perfect knowledge of the channel matrix H (perfect CSI) and that the transmitted signal F x̅ is subject to an average energy constraint. The columns of the matrix HF can be viewed as basis vectors that span a lattice, and we are interested in the minimum distance of this lattice. More precisely, for a given H, which F under an average energy constraint will maximize the minimum distance of the lattice HF? This particular question remains open within the theory of lattices. This work provides the solution for 2×2 matrices H; F. The answer is an F such that HF is a hexagonal lattice.
This paper presents the implementation of the mapper block in a faster-than-Nyquist (FTN) signaling transmitter. The architecture is look-up table (LUT) based and the complexity is reduced to a few ...adders and a buffer to store intermediate results. Two flavors of the architecture has been designed and evaluated in this article, one, a register based implementation for the buffer and the other using a random access memory (RAM). The tradeoff between the two is throughput versus area. The register based implementation is fast requiring only one clock cycle to complete the calculation (i.e a read, calculate and write back) for every incoming FTN symbol. However, it becomes prohibitive when systems with large number of sub-carriers (>64) is considered. The RAM based implementation provides a better solution in terms of area with slightly lower throughput. The mapper has been targetted for both FPGA (Xilinx Virtex-II Pro) and ASIC (130 nm standard cell CMOS) implementations. The design has been successfully tested on the FPGA and its output verified with the reference MATLAB model.
In this paper we consider the least time-frequency product necessary to transmit a small finite symbol packet such that the symbols can be independently detected. The system model assumed is offset ...QAM-OFDM, based on a finite duration pulse shape. The outcome is that the optimal pulse shape is of very short duration and that the optimal symbol allocation strategy is often to use as many subcarriers as there are symbols to transmit. Symbol packets up to 150 symbols are considered.
We investigate the performance of concatenated coding schemes based on faster than Nyquist (FTN) signaling over the AWGN channel. We test both serial and parallel concatenations. In serial ...concatenation the FTN signaling is considered as the inner encoder and the outer code is a rate b/c convolutional code. In parallel schemes we use two parallel Gaussian channels and transmit FTN pulse trains in both; here a precoding device turns out to be crucial. The convergence behaviour is analysed using EXIT charts. The overall spectral density of the schemes varies but is roughly 1-2 bit/s/Hz. The results, in terms of needed E b /N 0 for reliable communication versus spectral density, are very good
Faster-than-Nyquist (FTN) signaling is a method of improving bandwidth efficiency by transmitting information beyond Nyquist's orthogonality limit for interference free transmission. Previously have ...theoretically established that FTN can provide improved bandwidth efficiency. However, this comes at the cost of higher decoding complexity at the receiver. Our work has evaluated multicarrier FTN signaling for its implementation feasibility and complexity overhead compared to the gains in bandwidth efficiency. The work carried out in this research project includes a systems perspective evaluating performance, algorithm hardware tradeoffs and a hardware architecture leading to a silicon implementation of the decoder for FTN signaling. From the systems perspective, co-existence of FTN and OFDM based multicarrier system has been evaluated. OFDM being a part of many existing and upcoming broadband access technologies such as WLAN, LTE, DVB, this analogy is motivated. On the hardware aspect, the proposed architecture can accommodate both OFDM and FTN systems. The processing blocks in transmitter and receiver were designed for reuse and carry out different functions in the transceiver. Furthemore, the hardware could be configured to operate at varying bandwidth efficiencies (by FTN signaling) to exploit the channel conditions. The decoder implementation also considered block sizes and data rates to comply with the 3GPP standard. The decoding is carried out in as few as 8 iterations making it more practical for implementation in power constrained mobile devices. The decoder is implemented in 65nm CMOS process and occupies a total chip area of 0.8mm 2 .
We minimize the frequency and time occupancy of multicarrier binary linear modulation based on two-dimensional faster than Nyquist (FTN) signaling. FTN analysis provides the asymptotic time-frequency ...consumption per bit and prolate spheroidal wave analysis minimizes the side lobe occupancy. For both problems, an excellent choice is a Gaussian pulse, with some adjustment of the side lobes.
We consider the effect of symbol rate on the constrained capacity of linear modulation with a fixed spectral density. We show that constrained capacity grows with the symbol rate for some modulation ...pulses but shrinks with others. Sufficient conditions on the pulse are derived for the constrained capacity to be monotonically increasing with faster symbol rate. Most standard pulses fulfill these.
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