空时编码新方案：QO-STBC提升非相干检测性能

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本文主要探讨了空时编码在信息技术领域的一个重要进展，特别是基于Quasi-Orthogonal Space-Time Block Code (QO-STBC)的差分空间时间调制（Differential Space-Time Modulation，DSTM）技术。QO-STBC是一种创新的编码方案，它将联合调制与自定义星座集相结合，旨在提供全发射分集（full transmit diversity）功能，即使在非相干检测条件下也能实现高效通信。作者Chau Yuen、Yong Liang Guan和Tjeng Thiang Tjhung来自新加坡南洋理工大学和信息通信研究院，他们发现QO-STBC能够设计出比现有的基于正交空间时间块码（Orthogonal STBC）的DSTM方案具有更高编码速率的新系统。这种新方法的优势在于较低的解码复杂度，因为它只需要联合检测两个复数符号，而非像基于群码的DSTM那样涉及更复杂的处理。文章的核心内容包括： 1. **编码原理**：利用QO-STBC的特性，通过联合调制实现信号的多维编码，每个符号包含了多个空间和时间维度的信息，从而提高信息密度。 2. **设计准则**：研究人员提出了针对自定义星座集的设计准则，这些准则有助于构建能够提供宽广频谱效率、完整分集增益且满足最大编码增益的星座集。 3. **非相干检测下的性能**：由于采用的是非相干接收技术，使得QO-STBC的DSTM方案在实际应用中更具鲁棒性，即使在接收端的信道估计不准确的情况下，仍能保持良好的传输性能。 4. **比较优势**：相比于其他基于群码的DSTM，QO-STBC在编码速率和解码复杂度上的优势使其成为一种有竞争力的解决方案，尤其适合于那些对低复杂度和高数据速率需求的应用场景。 5. **潜在应用**：这项研究成果对于无线通信、卫星通信、移动通信等领域具有重要意义，可以提升系统的可靠性和有效性，特别是在移动终端和资源受限的环境中。这篇文章深入研究了空时编码中的QO-STBC在DSTM中的应用，提供了新的设计思路和优化方法，为未来无线通信系统的设计提供了有价值的技术支持。

Differential Transmit Diversity Based on

Quasi-Orthogonal Space-Time Block Code

Chau Yuen, Yong Liang Guan

School of Electrical and Electronic Engineering

Nanyang Technological University

Singapore

yuenchau@pmail.ntu.edu.sg, eylguan@ntu.edu.sg

Tjeng Thiang Tjhung

Institute for Infocomm Research

Singapore

tjhungtt@i2r.a-star.edu.sg

Abstract— By using joint modulation and customized

constellation set, we show that Quasi-Orthogonal Space-Time

Block Code (QO-STBC) can be used to form a new differential

space-time modulation (DSTM) scheme to provide full transmit

diversity with non-coherent detection. Our new scheme can

provide higher code rate than existing DSTM schemes based on

Orthogonal STBC. It also has a lower decoding complexity than

the other DSTM schemes, such as those based on Group Codes,

because it only requires a joint detection of two complex symbols.

We derive the design criteria for the customized constellation set

and use them to construct a constellation set that provides a wide

range of spectral efficiency with full diversity and maximum

coding gain.

Keywords - differential space-time modulation; low decoding

complexity; non coherent detection; quasi-orthogonal space-time

block code.

I. INTRODUCTION

In wireless communications, system performance is often

severely degraded by fading effects due to multi-path signal

propagation. Modulation techniques designed for multiple

transmit antennas, called space-time modulation or transmit

diversity can be used to reduce fading effects effectively. Early

transmit diversity schemes were designed for coherent

detection, with channel estimates assumed available at the

receiver. However, the complexity and cost of channel

estimation grow with the number of transmit and receive

antennas. Therefore the availability of transmit diversity

schemes that do not require channel estimation is desirable. To

this end, several differential space-time modulation (DSTM)

schemes have been designed [1-8].

Hughes has designed a DSTM based on group codes [1, 2];

Hochwald and Sweldens have designed a DSTM based on

unitary matrices [3]. Tarokh and Jafarkhani have proposed a

DSTM by using the Orthogonal Space-Time Block Code (O-

STBC) [4], while Ganesa and Stoica [8] provide another

DSTM also based on O-STBC but with a much simpler

decoding complexity. Hassibi et al. has proposed DSTM based

on Cayley code and Sp(2). Recently, Al-Dhahir gives a new

rate-two DSTM based on two parallel Alamouti O-STBCs for

four transmit antennas system [6]. Among them the scheme in

[8] has the simplest decoding complexity. However the DSTM

in [8] is based on the O-STBC, whose maximum achievable

code rate is limited to ¾ for four antennas and ½ for eight

antennas when used with complex constellations.

In this paper, we propose a new DSTM scheme that is

based on Quasi-Orthogonal STBC (QO-STBC) [9-13], to

provide full transmit diversity with higher code rate than that of

[8] and lower decoding complexity than other DSTM schemes

[1-7]. We will derive the design criteria and construct an

example constellation set for the proposed DSTM scheme. We

will also study its decoding complexity and decoding

performance in comparison with the existing schemes.

The organization of this paper is as follow, Section II

reviews the DSTM signal model and the decoding performance

criteria of DSTM. Section III proposes the new DSTM scheme

based on QO-STBC. And Section IV gives the performance

comparison. Finally Section V concludes the paper.

II. R

EVIEW OF DSTM

A. DSTM Signal Model

Consider a MIMO communication system, with N

transmit antennas and N

receive antennas. Let H

be the N

channel gain matrix at a time t. Thus the ij

element of H

the channel coefficient for the signal path from the j

transmit

antenna to the i

receive antenna. Let C

be the N

× P

codeword transmitted at a time t. Then, the received N

× P

signal matrix R

can be written as

tttt

=+RHCN

(1)

where

is the additive white Gaussian noise. In this paper, the

code length P is set equal to N

as in [1] and [8], so that the

transmitted codeword

is a square matrix.

At the start of the transmission, we transmit a known

codeword C

, which is a unitary matrix of size N

× N

. The

codeword

transmitted at a time t is differentially encoded by

1ttt−

=CCU

(2)

where U

is a unitary matrix (such that U

=I) called the code

matrix, that contains information of the transmitted data. Since

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