A New Construction of -QAM Golay Complementary Sequences

Low cost video sensors used for streaming video signals to help firefighters, require high bit rate due to uncompressed images. To increase spectral efficiency given a limited bandwidth, very high order constellations in high signal to noise ratio regimes can be used. However, noise is not the only factor effecting the high order constellations. These constellations are also sensitive to hardware impairments and system non‐linearities. Therefore, in this paper, the effect of carrier frequency offset (CFO) on the performance of an orthogonal frequency division multiplexing (OFDM) system with high order quadrature amplitude modulation (QAM) is studied. A closed form expression is derived for the maximum normalized residual CFO that an OFDM system with M ‐QAM constellation can resist to have an error free symbol detection. Finally, the suitability of common previous CFO estimation techniques such as the cyclic prefix based technique and the Moose technique in these systems are investigate. The results show that the maximum residual CFO that an OFDM system with M ‐QAM constellation can resist is proportional to the inverse of . The results also show that very large order QAM constellations such as 4096‐QAM are very sensitive to even small residual CFO values and their performance degrades, significantly. However, the bit error rate analysis indicate that the Moose CFO estimation technique can be used in these systems to compensate the CFO effect, accurately.

Complex field network coding has been shown to achieve a throughput of 1/2 symbol per user per channel use in a multi-way relay channel (MWRC). To achieve this throughput, a superimposed combination of user symbols must be distinguishable at the relay. In [1], precoding vectors were designed for an MWRC with all users employing the same rectangular quadrature amplitude modulation (QAM) constellation. These precoding vectors guarantee that every superimposed combination of user symbols at the relay is distinguishable and a QAM constellation is received. There are many precoding vectors with such properties. In this paper, we consider a more general problem in which each user can employ an arbitrary rectangular QAM constellation and we design a precoding vector for the users such that the power efficiency of the received rectangular QAM constellation at the relay is maximized.

A complementary M-ary orthogonal spreading (CMOS) architecture with orthogonal frequency division multiplexing (OFDM) is proposed to improve performance of bit-error rate (BER) and spectrum efficiency for high frequency (HF) communications. The CMOS-OFDM architecture is based on orthogonal complementary pairs with their central elements being zero. It is well known that complementary pairs theoretically reduce peak-to-mean envelope power ratio (PMEPR) of OFDM due to their ideal aperiodic auto-correlation properties. However, many practical OFDM applications, such as HF OFDM and IEEE 802.11, require that no data should be modulated to direct current (DC) subcarrier, which will destroy ideal properties of traditional complementary pairs and hence increase their PMEPRs. Compared with traditional complementary pairs, the proposed zero-centre complementary pairs (ZCCPs) in CMOS-OFDM architecture may maintain ideal properties and hence be more suitable for OFDM systems as long as zero element in the centre is modulated to DC subcarrier. The corresponding simulation results and numerical analyses over the HF fading channel modelled by ITU-R F.1487 are provided. Different from the previous researches on HF OFDM systems, the proposed HF CMOS-OFDM architecture using the constructed ZCCPs not only possesses excellent BER performance, but also may firmly resist PMEPR to 3 dB or near to 3 dB.

A low complexity maximum likelihood (ML) detection method is proposed for the square quadrature amplitude modulation (QAM) constellation. In order to reduce the implementation complexity of ML detection, set-partition, subset-selection, and subset-shift are recursively applied to the square QAM constellation. The estimated square QAM symbol is finally given in a closed form as a function of the received signal and the estimated channel. Complexity analysis and numerical simulation confirm that the proposed detection method reduces the implementation complexity substantially and achieves exactly the same performance as the conventional ML detection irrespective of the channel estimation error.

The peak-to-mean envelope power ratio (PMEPR) of a code employed in\northogonal frequency-division multiplexing (OFDM) systems can be reduced by\npermuting its coordinates and by rotating each coordinate by a fixed phase\nshift. Motivated by some previous designs of phase shifts using suboptimal\nmethods, the following question is considered in this paper. For a given binary\ncode, how much PMEPR reduction can be achieved when the phase shifts are taken\nfrom a 2^h-ary phase-shift keying (2^h-PSK) constellation? A lower bound on the\nachievable PMEPR is established, which is related to the covering radius of the\nbinary code. Generally speaking, the achievable region of the PMEPR shrinks as\nthe covering radius of the binary code decreases. The bound is then applied to\nsome well understood codes, including nonredundant BPSK signaling, BCH codes\nand their duals, Reed-Muller codes, and convolutional codes. It is demonstrated\nthat most (presumably not optimal) phase-shift designs from the literature\nattain or approach our bound.\n

Whenever a direct-sequence code-division multiple-access (DS-CDMA) signal is the sum of several components associated with different spreading codes [e.g., the DS-CDMA signal to be transmitted by the base station (BS) in the downlink or any multicode DS-CDMA signal], it has high envelope fluctuations and a high peak-to-mean envelope power ratio (PMEPR), setting strong linearity requirements for the power amplifiers. For this reason, it is desirable to reduce the envelope fluctuations of the transmitted signals. The use of clipping techniques combined with frequency-domain filtering was shown to be an effective way of reducing the envelope fluctuations (and, inherently, the PMEPR) of DS-CDMA signals, while maintaining the spectral occupation of the corresponding conventional DS-CDMA signals. To avoid PMEPR regrowth effects, the clipping and filtering operations can be repeated several times. However, the performance degradation due to nonlinear distortion effects on the transmitted signals can be relatively high, particularly when a very low PMEPR is intended (e.g., when a low clipping level and several iterations are adopted). This can particularly be serious if different powers are assigned to different spreading codes. To avoid significant performance degradation in these situations, we consider an improved receiver where there is an iterative estimation and cancellation of nonlinear distortion effects. Our performance results show that the proposed receiver allows significant performance improvements after just a few iterations, even when we have strong nonlinear distortion effects.

This letter considers waveform design of orthogonal frequency division multiplexing (OFDM) signal for radar applications, and aims at mitigating the envelope fluctuation in OFDM. A novel method is proposed to reduce the peak-to-mean envelope power ratio (PMEPR), which is commonly used to evaluate the fluctuation. The proposed method is based on the tone reservation approach, in which some bits or subcarriers of OFDM are allocated for decreasing PMEPR. We introduce the coefficient of variation of envelopes (CVE) as the cost function for waveform optimization, and develop an iterative least squares algorithm. Minimizing CVE leads to distinct PMEPR reduction, and it is guaranteed that the cost function monotonically decreases by applying the iterative algorithm. Simulations demonstrate that the envelope is significantly smoothed by the proposed method.

This paper considers waveform design of orthogonal frequency division multiplexing (OFDM) signal for radar applications, which aims at mitigating the envelope fluctuation in OFDM. A novel method is proposed to reduce the peak-to-mean envelope power ratio (PMEPR), which is commonly used to evaluate the fluctuation. The proposed method is based on the tone reservation approach, in which some bits or subcarriers of OFDM are allocated for decreasing PMEPR. We introduce the coefficient of variation of envelopes (CVE) as the cost function for waveform optimization, and develop an iterative least squares algorithm. Minimizing CVE leads to distinct PMEPR reduction, and it is guaranteed that the cost function monotonically decreases by applying the iterative algorithm. Simulations demonstrate that the envelope fluctuation is significantly smoothed by the proposed method.

In this paper, performance metric of orthogonal frequency division multiplexing (OFDM) system is analyzed over a composite fading channel, i.e., generalized K-fading channel. Here, OFDM system is considered which includes repetition code to enhance the wireless link performance with simplicity. Symbol error rate (SER) performance is evaluated using binary phase shift keying (BPSK) and 16-quadrature amplitude modulation (16-QAM) over generalized K-fading channel. This channel model considers Nakagami-m distribution to define multipath and gamma distribution to represent shadowing effects. Simulation results demonstrate that improved system performance can be achieved by using repetition code in severely faded environment. A comparative study of coded and uncoded system is also given in this paper. Consequently, SER performance is improved with the increase of shape parameters.

This paper presents the first concerted look at low correlation sequence families over quadrature amplitude modulation (QAM) constellations of size and their potential applicability as spreading sequences in a code-division multiple-access (CDMA) setting. Five constructions are presented, and it is shown how such sequence families have the ability to transport a larger amount of data as well as enable variable-rate signaling on the reverse link. Canonical family has period , normalized maximum-correlation parameter bounded above by , where ranges from in the 16-QAM case to for large . In a CDMA setting, each user is enabled to transfer bits of data per period of the spreading sequence which can be increased to bits of data by halving the size of the sequence family. The technique used to construct is easily extended to produce larger sequence families and an example is provided. Selected family has a lower value of but permits only -bit data modulation. The interleaved 16-QAM sequence family, has and supports 3-bit data modulation. The remaining two families are over a quadrature-pulse amplitude modulation (Q-PAM) subset of size of the -QAM constellation. Family has a lower value of in comparison with Family , while still permitting -bit data modulation. Interleaved Family , over the 8-ary Q-PAM constellation, permits 3-bit data modulation and interestingly achieves the Welch lower bound on .

Adaptive coded modulation (ACM) is a key technique to increase spectral as well as power efficiency for orthogonal frequency division multiplexing (OFDM) systems. In this paper, an efficient rate adaptive low density parity check (LDPC) coded modulation (RALCM) algorithm is proposed, which maximizes the payload rate for OFDM systems under the constraint of the given transmit power and the target bit error rate (BER). Taking advantage of the two dimensional look up table for the signal to noise ratio (SNR) thresholds, the RALCM algorithm assigns different combinations of the LDPC code rates and quadrature amplitude modulation (QAM) modulations for subcarriers according to the channel frequency response (CFR). Both theoretical analysis and computer simulation show that the proposed algorithm not only efficiently improves the payload rate of the LDPC coded OFDM system over frequency selective fading channels, but also inherently reduces the computational complexity of the system optimization.

Orthogonal Frequency Division Multiple Access (OFDMA) with Dynamic spectrum allocation (DSA) is able to provide a wide range of data rate requirements. This paper is focused on the design of preamble sequences in OFDMA systems with low peak-to-mean envelope power ratio (PMEPR) property in the context of DSA. We propose a systematic preamble sequence design which gives rise to low PMEPR for possibly non-contiguous spectrum allocations. With the aid of Golay-Davis-Jedwab (GDJ) sequences, two classes of preamble sequences are presented. We prove that their PMEPRs are upper bounded by 4 for any DSA over a chunk of four contiguous resource blocks.

Clipping is a popular method to overcome large peak-to-mean envelope power ratios (PMEPRs) in orthogonal frequency-division multiplexing (OFDM) systems, but it results in nonlinear distortion, which degrades signal detection performance. In this paper, clipping effects on signal detection with a simple channel estimation in OFDM are investigated, signal-to-noise and distortion ratio (SNDR) results of detected signals are derived, and symbol error rates (SERs) of clipped OFDM in frequency selective Rayleigh fading channels are evaluated. The evaluated SER results are supported by simulations.

In this paper, we consider out-of-band radiations caused by high sidelobes in orthogonal frequency division multiplexing (OFDM) system. Suppression of sidelobes in OFDM system allows higher spectral efficiency and less interference with existing legacy systems in OFDM based overlay system. We combine different sidelobe suppression techniques to suppress the sidelobes in OFDM system. The multiple-choice sequence (MCS) is combined with cancellation carriers (CCs) and also MCS is combined with subcarrier weighting (SW) technique. MCS is applied prior to CCs or SW techniques. Simulation results show that combining MCS with CCs and MCS with SW techniques the sidelobes in OFDM system can be significantly reduced, which allow a successful co-existance between OFDM overlay system and an existing legacy system.

The typical subcarrier modulation schemes used in orthogonal frequency division multiplexing (OFDM) system includes; binary phase shift keying (BPSK), quadrature phase shift keying (QPSK) and quadrature amplitude modulation (QAM). This paper analyses the performance of OFDM system that uses various number of modulation QAM constellation points over various fading channels. Simulation is done for various numbers of QAM (8 to 64-points) and with various Doppler frequency values (5 to 500 Hz) over flat and frequency selective fading channels. Results show that the best performance of OFDM system is with the number of QAM of 8 and maximum Doppler shift (MDS) of 5 Hz at all channels.