Dalin Zhu

Residue number system arithmetic assisted coded frequency-hopped OFDMA

We propose an RNS arithmetic-based FH pattern design approach that is well suited and easy to implement for practical OFDMA systems. The proposed FH scheme guarantees orthogonality among intracell users while randomizing the intercell interferences and providing frequency diversity gains. We present detailed construction procedures and performance analysis for both independent and cluster hopping scenarios. Using simulation results, we demonstrate the gains due to frequency diversity and intercell interference diversity on the system bit error rate (BER) performance. Furthermore, the BER performance gain is consistent across all cells unlike other FH pattern design schemes such as the Latin squares (LSs-)-based FH pattern design where wide performance variations are observed across cells.

On the performance of redundant residue number system codes assisted STBC design

In this paper, we propose a novel application of Redundant Residue Number System (RRNS) codes to Space-Time Block Codes (STBCs) design. Based on the so-called “Direct-Mapping” scheme, the link between residues and complex signal constellations is optimized. We derive upper bounds on the codeword error probability of RRNS-STBC and characterize its achievable diversity gain assuming maximum likelihood decoding (MLD). The knowledge of apriori probabilities of residue generation is utilized to implement a probability based Distance-Aware Direct Mapping scheme for M-ary modulation which further improves the error performance of the RRNS-STBC coding scheme.

Trellis Exploration Algorithm Aided Unitary Precoder Design for Maximizing MIMO Capacity With Limited Feedback

In this letter, we present a novel approach to determine limited feedback-based unitary precoder for maximizing single user (SU)-MIMO capacity. Specifically, a polyphase unitary precoding matrix is custom designed via the trellis exploration algorithm employing system capacity as the metric to maximize. Since the trellis exploration algorithm operates on a finite set of phases, information regarding the optimal precoder is fed back to the transmitter using a limited number of bits.

Residue Number System Arithmetic Aided Frequency-Hopping Pattern Design in Coded OFDMA

In this paper, we propose an RNS arithmetic based FH pattern design approach that is well suited and easy to implement for practical OFDMA systems. The proposed RNS aided FH scheme not only guarantees orthogonality among intra-cell users but also randomizes inter-cell interference. We present detailed construction procedures and performance anal- ysis for both independent and cluster hopping scenarios. We also demonstrate the gains due to frequency diversity and inter- cell interference diversity on the system bit error rate (BER) performance via simulations. The proposed scheme offers BER performance gain that is consistent across all cells unlike other FH pattern design schemes such as the Latin Squares (LS) based FH pattern design, where wide performance variations are observed across cells.

Peak-to-Average Power Ratio Reduction in MIMO-OFDM with Trellis Exploration Algorithm

In this paper, we propose a multi-layer precoding scheme to reduce PAPR in MIMO-OFDM systems. Specifically, an outer-layer polyphase precoding matrix P is custom designed using the trellis exploration algorithm that was previously applied to the design of spreading sequences for CDMA systems. The algorithm determines the P matrix that results in the minimum aperiodic autocorrelation (and therefore minimum PAPR) among transmitted OFDM data symbols. Simulation results illustrate that the proposed multi-layer precoding scheme can not only significantly lower the PAPR in a MIMO-OFDM, but also well preserve the performance gains that are obtained by inner-layer precoding. Index Terms—PAPR, multi-layer precoding, MIMO-OFDM, trellis exploration algorithm

Residue Number System Arithmetic-Inspired Hopping-Pilot Pattern Design

In this paper, we propose a novel application of residue number system (RNS) arithmetic in designing hopping-pilot patterns for cellular downlink orthogonal frequency-division multiple access (OFDMA). By hopping the scan lines in either the time or the frequency domain, RNS-based pilot patterns fulfill the Nyquist sampling theorem. That is, by using RNS-based pilot patterns, the channels delay-Doppler response can fully be reconstructed without severe aliasing. In addition to channel estimation, our proposed scheme can achieve other objectives, such as device/cell identification and time-frequency synchronization. We show that the RNS-based approach has more pairs of hopping-pilot patterns that are collision free than the Costas-array-based method. This is helpful in not only mitigating intra-/intercell interference but also identifying multiple devices in a multicell multiantenna environment. Moreover, hopping in time increases the pilots time support, which, in turn, enables quick initial acquisition of time-frequency offsets.

Trellis Exploration Algorithm Aided Precoder Design in Maximizing MIMO Capacity with Limited Feedback

In this paper, a novel precoder design method is proposed for maximizing MIMO capacity. Specifically, under equal power allocation, we employ the trellis exploration algorithm to design the precoding matrix such that the condition number of the resulting effective channel matrix is minimized. Since the trellis exploration algorithm operates on a finite set of phases, the polyphase precoder is first custom designed at the receiver. Then, a small number of bits indicating phase indices of the corresponding precoding matrix is fed back to the transmitter. We show that for a 2 × 2 MIMO, only 8 feedback bits are necessary to achieve desired performance gain. Simulation results demonstrate that the proposed approach outperforms the well-known water-filling scheme at high SNR in terms of ergodic capacity.

Multiuser MIMO capacity with limited feedback trellis exploration based precoder

In this paper, a linear trellis based precoder technique is proposed for maximizing multiuser MIMO capacity. We consider MIMO multiple access channel with inter symbol interference (ISI). We use the trellis exploration algorithm to form a precoding matrix that minimizes the interference from other users by allocating power in the appropriate eigen modes for each user. Employing a finite number of phases, the precoder matrix for each user is first custom designed at the receiver. Then a bit sequence indicating the phase indices of the optimized precoding matrix for the corresponding user is fed back to the transmitter. We show that under limited feedback, the sum rate capacity achieved is comparable to the optimal sum-rate capacity employing the well-known water filling solution with complete channel knowledge at the transmitter for spatio-temporal vector coding (STVC). Our simulations for various multiuser MIMO cases, show that the per user precoding strategy achieves desirable performance gain with limited feedback and equal user power allocation in terms of ergodic capacity.

Full length article: Maximizing capacity with trellis exploration aided limited feedback precoder design for multiuser MIMO-MAC

In this paper, a linear trellis based precoding technique is proposed for maximizing the multiuser MIMO capacity in a multiple access channel with inter symbol interference (ISI). We use the trellis exploration algorithm to design a precoding matrix that minimizes the interference from other users by allocating power in the appropriate eigenmodes. Employing a finite number of phases, the precoder matrix for each user is first custom designed at the receiver. Then a bit sequence indicating the phase indices of the optimized precoding matrix elements for the corresponding user is fed back to the transmitter. We show that under this approach, the sum rate capacity achieved is comparable to the optimal sum-rate capacity employing the well-known water filling solution with complete channel knowledge at the transmitter for spatio-temporal vector coding (STVC). Our simulations for various multiuser MIMO cases, show that the per user precoding with limited feedback and equal power allocation strategy achieves desirable capacity gains relative to the eigenbeamforming and Grassmannian precoding.

Limited Feedback-Based Unitary Precoder Design in Rician MIMO Channel via Trellis Exploration Algorithm

It is well known that in practice, MIMO channels usually exhibit strong line-of-sight (LoS) components. However, common codebook designs in precoded MIMO rely heavily on the assumption of i.i.d Rayleigh fading. Therefore, designing practical unitary precoders that are suited for realistic channel condition (such as Rician MIMO channel) becomes an interesting topic to investigate. In this paper, we propose to use trellis exploration algorithm to accomplish this objective by adapting each entry of the precoding matrix to instantaneous channel realizations. Since trellis search is an on-line learning approach, our proposed precoding scheme is more adaptive to variations in channel propagations than off-line designed codebooks. Specifically, we use simulation results to show that in Rician MIMO channel, our proposed approach results in better performance than Grassmannian line/space packing and typical DFT codebook design in terms of ergodic capacity, under the same amount of feedback bits.