Sujit Jos

Low-complexity direction estimation techniques for fast beamforming training in millimeter wave multiantenna systems

This paper explores a novel approach for beamforming (BF) training in millimeter wave (mmWave) multiantenna communication systems. The contribution of this paper is in the following aspects: i) This paper proposes a fast BF training procedure building on the novel concept of beamcoding for the estimation of the optimal direction of arrival (DoA) and direction of departure (DoD). Briefly, the beamcoding scheme facilitates the identification of DoA/DoD at the receiver/transmitter based on a set of orthogonal codes. ii) Building on the properties of a special class of orthogonal codes called constant amplitude zero autocorrelation(CAZAC) sequences, this paper proposes a low-complexity implementation of beamcoding procedure to facilitate BF training. We emphasize that the proposed beamcoding schemes can be implemented at the transmitter/receiver with the help of only a single radio frequency (RF) chain with a set of analog phase shifters. Notably, the proposed method is not restricted to just mmWave communication systems, and can be applied to any generic system involving multiantenna transceivers. Simulation results are presented to demonstrate the efficacy of our proposed idea.

Method of Generating Multiple Sets of Orthogonal Codes with Wide Choice of Spreading Factors

This paper presents a generic method to construct multiple sets of orthogonal codes for application in direct sequence spread spectrum systems. The plurality of orthogonal sets is generated using any single two-level autocorrelation sequence of period one less than the desired spreading factor of the orthogonal codes. The proposed method hence generates orthogonal codes of all spreading factors for which a corresponding two-level autocorrelation sequence exists. The resulting orthogonal sets with wide choice of spreading factors is desirable in synchronous direct sequence spread spectrum systems. The sets can be generated such that they do not contain the codeword with single polarity as in the case of Walsh-Hadamard codes and orthogonal sets generated from cyclic shifts of two-level autocorrelation sequences. This renders all codes in the generated sets with an effective spreading gain. The generation method also encompasses a procedure to generate N-1 sets with low inter-set correlation for application to oversaturated spread spectrum systems.

Sub-sampled OFDM based sub-band ultra-wideband system

In sub-band ultra-wideband (SUWB) systems, the use of spreading codes in conjunction with sub-banding enables energy efficient reduced sampling rate receiver designs. In this work, the orthogonal frequency division multiplexing (OFDM) technique is proposed for SUWB systems as a means to mitigate the multipath fading effects of the channel. The OFDM demodulation performed at the sub-sampled rate with reduced number of discrete Fourier transform (DFT) points provides scope for low power receiver implementations. Moreover, OFDM improves the flexibility as bandwidth resources can be allocated with improved granularity at integral multiples of the OFDM sub-channel bandwidth. The requisite correlation properties of the spreading codes is relaxed in the proposed OFDM-SUWB system and more number of spreading codes can be used when compared to the existing SUWB system. Also, a simple channel estimation method exploiting the low complexity advantage of the inherent spreading code based receiver is proposed. Simulation results in terms of the bit error rate (BER) performance are presented over the IEEE 802.15.4a channel models and also comparisons with the multi-band OFDM (MB-OFDM) system are made demonstrating the usefulness of the proposed scheme.

A low complexity algorithm for sampling clock-offset compensation in low power WPAN receivers

This paper presents a low complexity algorithm for compensating the sampling-clock frequency offset encountered in short-range WPAN receivers. The proposed algorithm leverages on the pulse shaping information in the transmitted signal to identify erroneous samples resulting from the sampling-clock frequency offset and then compensates for the same. Simulation results demonstrate that the proposed algorithm almost completely compensates for offsets of magnitudes specified by WPAN standards.

Method of simultaneous transmission to coherent and non-coherent receivers using ternary sequences

In this paper, we explore a method for simultaneous tranmission to coherent and non-coherent receivers, based on ternary sequences. In many communication scenarios, the transmitters are required to support both coherent and non-coherent forms of reception thereby requiring the transmission protocols to be designed such that the transmitted data is decoded reliably at both coherent and non-coherent receivers. Further, in such scenarios, for practical purposes, the transmitter is assumed to be agnostic to the type of the intended receiver, making the design more challenging. Thus motivated, we propose a transmission mechanism for simultaneous reception by coherent and noncoherent receivers. This transmission is enabled by ternary codes, i.e., codes over the ternary alphabet: {-1, 0, +1}. The design of these ternary codes, which exhibit good correlation properties for both coherent and non-coherent reception is a major contribution of this paper. Simulation results show that the proposed codes provide almost similar performance as the optimal codes meant for the respective receiver types.

A Note on "A Novel ZCZ Code Based on m-Sequences and its Applications in CDMA Systems"

This short communication shows that zero correlation zone sequences could be generated by using any odd-length binary sequence with ideal two-level autocorrelation function in place of the m-sequence using the exact same procedure proposed in the original paper. This removes the restriction on the spreading factor of the m-ZCZ sequences which could assume only the form 2n for some integer n. The spreading factor can now be any N for which an ideal two-level autocorrelation sequence of period N - 1 exists.