Abstract
Integrating the strengths of multicarrier (MC) modulation and code division multiple access (CDMA), MC-CDMA systems are of great interest for future broadband transmissions. This paper considers the problem of channel identification and signal combining/detection schemes for MC-CDMA systems equipped with multiple transmit antennas and space-time (ST) coding. In particular, a subspace-based blind channel identification algorithm is presented. Identifiability conditions are examined and specified which guarantee unique and perfect (up to a scalar) channel estimation when knowledge of the noise subspace is available. Several popular single-user based signal combining schemes, namely the maximum ratio combining (MRC) and the equal gain combining (EGC), which are often utilized in conventional single-transmit-antenna-based MC-CDMA systems, are extended to the current ST-coded MC-CDMA (STC-MC-CDMA) system to perform joint combining and decoding. In addition, a linear multiuser minimum mean square error (MMSE) detection scheme is also presented, which is shown to outperform the MRC and EGC at some increased computational complexity. Numerical examples are presented to evaluate and compare the proposed channel identification and signal detection/combining techniques.
Highlights
Multicarrier (MC) technologies (e.g., [1] and the references therein), in particular OFDM, are considered very promising for future broadband data services in fading environments
We extend two signal combining schemes, namely the maximum ratio combining (MRC) and the equal gain combining (EGC) which are often utilized in conventional single-transmit-antenna-based MC-code division multiple access (CDMA) systems [11], to STC-multicarrier CDMA (MC-CDMA) to perform joint combining and decoding
While both MRC and EGC are singleuser detection schemes based on per-subcarrier combining, we present a linear minimum mean square error (MMSE) multiuser detector which performs joint-subcarrier combining and decoding
Summary
Multicarrier (MC) technologies (e.g., [1] and the references therein), in particular OFDM (orthogonal frequency division multiplexing), are considered very promising for future broadband data services in fading environments. While orthogonal spreading codes are often used to maintain orthogonality among different user transmissions in the forward link of single-carrier CDMA systems, for example, IS-95 [14], user orthogonality is usually lost in MC-CDMA systems when operating in frequency selective environments which gives rise to multiuser interference (MUI) [11]. We extend two signal combining schemes, namely the maximum ratio combining (MRC) and the equal gain combining (EGC) which are often utilized in conventional single-transmit-antenna-based MC-CDMA systems [11], to STC-MC-CDMA to perform joint combining and decoding. Vectors (matrices) are denoted by boldface lower (upper) case letters; all vectors are column vectors; superscripts ∗, T, and H denote the complex conjugate, transpose, and conjugate transpose, respectively; IN denotes the N × N identity matrix; 0 denotes an all-zero vector/matrix; ran(·) denotes the range space of a matrix argument; E{·} denotes the statistical expectation; ⊗ denotes the matrix Kronecker product [29]; and diag{·} denotes a diagonal matrix
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