Название: Spatial Multidimensional Cooperative Transmission Theories And Key Technologies
Автор: Lin Bai
Издательство: Ingram
Жанр: Зарубежная компьютерная литература
isbn: 9789811202476
isbn:
where E[|si|2] = Ei and E[|n|2] = N0. If the received power of the two signals is assumed to be the same, namely E1 = E2, and the channel gain is also assumed to be the same, namely |h1|2 = |h2|2, then the SINR of signal s1 will be less than 0 dB, which brings great difficulty to the signal detection.
Successive interference cancellation is an alternative method to improve the performance of signal detection. Assuming E1 > E2, the SINR of s1 is relatively high at this time, and it is possible to detect s1 first. Let
This detection method is called Successive Interference Cancellation (SIC) and can be applied to MIMO joint signal detection.
In order to realize SIC, QR decomposition plays an important role in the SIC-based detection process.10, 11 QR decomposition is a common method of matrix decomposition, which can be decomposed into the product of an orthogonal matrix and an upper triangular matrix. And how the 2 × 2 MIMO system performs QR decomposition will be introduced first in this section.
Assume that there is a 2 × 2 channel matrix H = [h1 h2], where hi represents the ith column vector of H. Define the inner product of the two vectors to be
where
According to the linear relationship described by Eq. (2.154), it can be judged that [h1 h2] and [r1 r2] can span the same subspace. And if ri is a non-zero vector (i = 1, 2), it can be found that
where qi = ri/||ri||. Based on Eq. (2.156), an orthogonal matrix Q = [q1 q2] and an upper triangular matrix
The successive interference cancellation of the received signal can be performed according to the QR decomposition of the channel matrix. This section only discusses the case where the channel matrix H is a square matrix or a thin matrix (M ≤ N) whose number of rows is larger than the number of columns.
1. H is a square matrix
H can be decomposed into an M × M unitary matrix Q and an M × M upper triangular matrix R.
where rp,q is defined as the (p, q)th element of R. By the premultiplication of QH, the received signal can be expressed as
where QHn is a zero-mean CSCG random vector. QHn has the same statistical property as n, and hence, n can be used directly to replace QHn. As a result, Eq. (2.158) can be transformed into
If xk and nk are defined as the kth element of x and n, the above equation can be expanded as follows:
Therefore, SIC detection can be carried out
2. H is a thin matrix
The QR decomposition of H is
where M < N and Q is an unitary matrix. We have
Furthermore,
Since the received signal {xM+1, xM+2, . . . , xN} does not contain any useful information, it can be ignored directly. On this basis, Eqs. (2.161) and (2.164) are identical in form, and thus, successive interference cancellation can be realized. First, sM can be detected based on xM.
If
The above equation shows that since there is no interference term in the detection of sM, the influence of sM can be eliminated during СКАЧАТЬ