08-12-2012, 02:24 PM
Uncoordinated Beamforming for Cognitive Networks
[attachment=43071]
Abstract
In this paper, we propose jointly-optimized beamforming
algorithms for cognitive networks to maximize the
achievable rates, where primary and cognitive users share the
same spectrum and are equipped with multiple antennas. We
consider the transmission of a single information stream in
both primary and secondary links. No coordination is required
between the primary and cognitive users and the interference
cancellation is done at the cognitive user. Specifically, the beamforming
vectors of the cognitive link are designed to maximize
the achievable rate under the condition that the interference both
at the primary and cognitive receivers is completely nullified.
Furthermore, it is proved that the achievable rate of a general.
INTRODUCTION
THE opportunistic use of the wireless spectrum has been a
hot research topic in the wireless communications community
in recent years due to the intense competition for the
use of spectrum at frequencies below 3 GHz [1]. In particular,
cognitive networks have received much attention [2]. Related
works on capacity region have been studied extensively, for
example, in [3]–[6]. A cognitive network consists of a number
of traditional wireless service subscribers and the so-called
cognitive users. The traditional wireless service subscribers
have the legacy priority access to the spectrum and are usually
called the primary users in the literature. On the other hand,
cognitive users, which are also known as the secondary users,
are allowed to access the spectrum only if communication
does not create significant interference to the licensed primary
users. This can be achieved in several ways as discussed in
[7] and references therein. For example, the cognitive user
can transmit concurrently with the primary users under an
enforced spectral mask. Another strategy, commonly referred
to as spectrum sensing, is to have the cognitive users monitor
the spectrum and access it when an unused slot is detected.
NETWORK AND CHANNEL MODELS
Consider a cognitive network with a single primary user
and a single cognitive (secondary) user as depicted in Fig. 1.
Each user consists of a transmitter and a receiver.
Furthermore, we assume that the antennas are uncorrelated and
the channel is frequency non-selective which can be easily
achieved by using multiple-input multiple-output orthogonal
frequency division multiplexing (MIMO-OFDM) [23]. Note
that, however, our solution is not directly related to the channel
model. Once channel information is known, the cognitive
transmitter and receiver can compute the transmit/receive
beamforming vectors using the proposed algorithms. The
MIMO channel between the primary transmitter and receiver
is denoted by W whereas the one between the secondary
transmitter and receiver is denoted by H. The interference
channel from the primary transmitter to the secondary receiver
is denoted by D and the interference channel from the
secondary transmitter to the primary receiver is denoted by
G.
CONCLUSION
In this paper, we considered interference cancellation and
rate maximization via uncoordinated beamforming in a cognitive
network which consists of a single primary and secondary
user. The secondary cognitive user was allowed to transmit
concurrently with the primary licensed user. The beamforming
vectors of the cognitive user were designed such that the
interference is completely nullified both at the primary and
secondary receivers while maximizing the rate of the cognitive
link. Since no interference is created at the primary receiver,
traditional approaches can be used to design the beamforming
vectors or precoding matrices of the primary user. Three
approaches were proposed for the design of the beamforming
vectors of the cognitive link. The optimal beamforming
solution for the special case of NC
r = 2 was also derived.
For NC
r > 2, we resorted to numerical methods to solve the
optimization problem.
[attachment=43071]
Abstract
In this paper, we propose jointly-optimized beamforming
algorithms for cognitive networks to maximize the
achievable rates, where primary and cognitive users share the
same spectrum and are equipped with multiple antennas. We
consider the transmission of a single information stream in
both primary and secondary links. No coordination is required
between the primary and cognitive users and the interference
cancellation is done at the cognitive user. Specifically, the beamforming
vectors of the cognitive link are designed to maximize
the achievable rate under the condition that the interference both
at the primary and cognitive receivers is completely nullified.
Furthermore, it is proved that the achievable rate of a general.
INTRODUCTION
THE opportunistic use of the wireless spectrum has been a
hot research topic in the wireless communications community
in recent years due to the intense competition for the
use of spectrum at frequencies below 3 GHz [1]. In particular,
cognitive networks have received much attention [2]. Related
works on capacity region have been studied extensively, for
example, in [3]–[6]. A cognitive network consists of a number
of traditional wireless service subscribers and the so-called
cognitive users. The traditional wireless service subscribers
have the legacy priority access to the spectrum and are usually
called the primary users in the literature. On the other hand,
cognitive users, which are also known as the secondary users,
are allowed to access the spectrum only if communication
does not create significant interference to the licensed primary
users. This can be achieved in several ways as discussed in
[7] and references therein. For example, the cognitive user
can transmit concurrently with the primary users under an
enforced spectral mask. Another strategy, commonly referred
to as spectrum sensing, is to have the cognitive users monitor
the spectrum and access it when an unused slot is detected.
NETWORK AND CHANNEL MODELS
Consider a cognitive network with a single primary user
and a single cognitive (secondary) user as depicted in Fig. 1.
Each user consists of a transmitter and a receiver.
Furthermore, we assume that the antennas are uncorrelated and
the channel is frequency non-selective which can be easily
achieved by using multiple-input multiple-output orthogonal
frequency division multiplexing (MIMO-OFDM) [23]. Note
that, however, our solution is not directly related to the channel
model. Once channel information is known, the cognitive
transmitter and receiver can compute the transmit/receive
beamforming vectors using the proposed algorithms. The
MIMO channel between the primary transmitter and receiver
is denoted by W whereas the one between the secondary
transmitter and receiver is denoted by H. The interference
channel from the primary transmitter to the secondary receiver
is denoted by D and the interference channel from the
secondary transmitter to the primary receiver is denoted by
G.
CONCLUSION
In this paper, we considered interference cancellation and
rate maximization via uncoordinated beamforming in a cognitive
network which consists of a single primary and secondary
user. The secondary cognitive user was allowed to transmit
concurrently with the primary licensed user. The beamforming
vectors of the cognitive user were designed such that the
interference is completely nullified both at the primary and
secondary receivers while maximizing the rate of the cognitive
link. Since no interference is created at the primary receiver,
traditional approaches can be used to design the beamforming
vectors or precoding matrices of the primary user. Three
approaches were proposed for the design of the beamforming
vectors of the cognitive link. The optimal beamforming
solution for the special case of NC
r = 2 was also derived.
For NC
r > 2, we resorted to numerical methods to solve the
optimization problem.