164
China Communications
●
Supplement No.1 2014
Interference Alignment Based on Subspace Tracking in
MIMO Cognitive Networks with Multiple Primary Users
XIE Xianzhong, XIONG Zebo
Chongqing Key Lab of Computer Network and Communication Technology, Chongqing University of Posts and Telecommunications,
Chongqing 400065, China
Abstract: The interference alignment (IA) algorithm
based on FDPM subspace tracking (FDPM-ST IA)
is proposed for MIMO cognitive network (CRN)
with multiple primary users in this paper. The
feasibility conditions of FDPM-ST IA is also got.
Futherly, IA scheme of secondary network and IA
scheme of primary network are given respectively
without assuming a priori knowledge of interference
covariance matrices. Moreover, the paper analyses
the computational complexity of FDPM-ST IA.
Simulation results and theoretical calculations show
that the proposed algorithm can achieve higher sum
rate with lower computational complexity.
Key words: MIMO cognitive networks; multiple
primary users; subspace tracking; interference
alignment; sum rate; computational complexity
I. INTRODUCTION
There are serious interferences in MIMO cognitive
radio networks (CRN), which not only includes all
interferences in general wireless networks, but also
interferences of between secondary users (SUs) and
primary users (PUs). Interference alignment (IA) is
a hot research topic in the interference management
[1]. Recently, IA has been applied to CRN to
remove interference and enhance capacity [2-6].
The distributed interference alignment (DIA)
based on minimizing interference of the transmitter
to undesired receiver is given in [2]. DIA employs
with the characteristics of reciprocal network,
and is realized by iteration processing. Ref. [3]
introduces the opportunistic interference alignment
(OIA), under the condition of the same frequency
and time, allowing SUs use unused dimension of
PUs to transmit information, SUs can eliminate
the interference to the PUs through interference
alignment. In cellular network, the IA based
Interference Subspace Tracking (IST-IA) is given
in [4]. When the User Equipment (UE) and the
Base Station (BS) are without a priori knowledge
of the interference covariance matrix, IST-IA
updates directly the precoding and interference
suppression matrices based on received signals by
a minor subspace tracking algorithm. IST-IA yields
a good trade-off among throughput gain, training
overhead and computational complexity. On the
basis of [4], a practical IA algorithm is developed
via the minor subspace tracking that utilizes the
fast data projection method (FDPM) in [5]. But [5]
does not take the interference of PUs to SUs into
account, and ignores that there are multiple primary
users in CRN. According to the results of [6], PUs
interference to SUs can not be ignored in CRN with
multi-PUs. It is clear that the system becomes more
complex with the increasing of the primary users,
and the realization of the interference alignment is
more difcult.
Based on Ref. [4] and [5], this paper explores
interference alignment scheme in MIMO CRN with
multi-PUs. We propose the interference alignment
algorithm based on FDPM subspace tracking
(FDPM-ST IA). FDPM-ST IA is an improved
scheme of [5] to multiple primary users in MIMO
CRN with considering the PUs interference to SUs,
is also an extension scenario of the IST-IA in [4].
Unlike traditional subspace tracking algorithm,
FDPM-ST IA aligns the transmitted signal of each
secondary transmitter into the null space of the
channel matrix from the primary transmitter. Thus
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