非分时主用户状态切换下全双工认知无线系统容量优化

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本文探讨了全双工认知无线电系统中的容量最大化问题，其中主要用户（Primary User, PU）的状态是非分时的，并且可能在任一时间点在一帧时间内发生变化。传统上，认知无线电系统假设PU状态是分时的，然而现实情况中，这种变化性增加了系统的动态性挑战。首先，作者针对非分时的PU状态，推导出了感知概率的计算方法。由于非分时状态可能导致信道环境的不确定性，对随机出现的PU活动进行准确的感知至关重要。这涉及到对信道噪声、干扰以及SU（Secondary User）与PU信号交互的影响进行建模。接着，论文重点研究了在考虑非分时状态变化的情况下，如何优化传输参数以最大化SU的容量。具体来说，包括决定SU的帧长度、发射功率以及针对静默和活跃PU状态设置的两个检测阈值。通过对这些参数的联合优化，论文旨在找到一个在实际情况下具有较低计算复杂度但仍能接近最优性能的解决方案。通过数值仿真，研究结果展示了非分时状态的考虑对于提高系统效率的重要性。相比于理想化的分时PU状态假设，采用非分时策略可以显著提升SU的通信速率，使得在处理实时变化的环境时，系统表现出更好的适应性和容量利用率。研究的关键术语包括：认知无线电（Cognitive Radio）、全双工（Full-Duplex）、非分时（Non-Slotted）、容量优化（Capacity Optimization）以及频谱感知（Spectrum Sensing）。这一研究对于设计和实现高效能的认知无线电网络具有重要意义，它强调了在实际通信环境中考虑系统动态性的必要性，从而推动了无线通信领域的技术进步。

1890 IEEE COMMUNICATIONS LETTERS, VOL. 22, NO. 9, SEPTEMBER 2018

Capacity Maximization in Full-Duplex Cognitive Radio Systems With

Non-Slotted Primary User State Change

Wenjun Xu , Senior Member, IEEE, Jiji Tang, Zhen Wang, and Li Guo, Member, IEEE

Abstract—This letter considers the capacity maximization

problem in full-duplex cognitive radio systems, where the state of

primary user (PU) is non-slotted and may change at any time in

one slot. First, the sensing probabilities are derived in the case

of non-slotted PU state. Then, slot duration, transmit power,

and two detection thresholds, respectively, corresponding to two

cases that secondary user (SU) is silent or active, are jointly

optimized to maximize SU’s capacity. Numerical results show

that the proposed algorithm can achieve the near-optimal solution

with a low computational complexity and a considerably higher

capacity, compared with the ideal assumption of slotted PU state,

can be obtained by considering the non-slotted state change.

Index Terms—Cognitive radio, full-duplex, non-slotted, capac-

ity optimization, spectrum sensing.

I. INTRODUCTION

ITH the rapid development of wireless communica-

tion networks, the available spectrum resources have

become increasingly scarce. Cognitive radio (CR) technology

has emerged to alleviate the shortage problem of spectrum

resources, usually by allowing secondary user (SU) to oppor-

tunistically access the available bands which are not occupied

by PU [1]. Most of the existing work concerning CR networks

is based on half-duplex (HD) mode, which adopts “listen

before talk” (LBT) protocol. However, this mode may lead

to discontinues transmission and longer collision duration

since CR systems can not detect the collision immediately

if a collision occurs during data transmission [2]. Recently,

the full-duplex (FD) communication mode is proposed, which

adopts “listen and talk” (LAT) protocol and allows SU to sense

radio spectrum while transmitting data. Owing to the great

progress of self-interference cancelation (SIC) technologies,

the residual self-interference (RSI) can now be suppressed to a

much lower level so that the FD transmission mode is feasible

in practical CR systems [3], e.g., [2] validates FD technology

can solve the discontinuous transmission problems effectively

and [3] states FD technology can increase throughput and

reduce collisions as opposed to HD technology.

Manuscript received May 25, 2018; accepted July 3, 2018. Date of pub-

lication July 11, 2018; date of current version September 8, 2018. This

work is supported in part by the National Natural Science Foundation of

China (61471059, 61790553), in part by the Fundamental Research Funds

for the Central Universities (2014ZD03-01), and in part by the Special

Youth Science Foundation of Jiangxi (20133ACB21007). The associate editor

coordinating the review of this letter and approving it for publication was

N. Tran. (Corresponding author: Wenjun Xu.)

W. Xu, J. Tang, and L. Guo are with the Key Laboratory of Universal

Wireless Communications, Ministry of Education, Beijing University of Posts

and Telecommunications, Beijing 100876, China (e-mail: wjxu@bupt.edu.cn).

Z. Wang is with the School of Information Engineering, Nanchang Univer-

sity, Nanchang 330031, China.

Digital Object Identiﬁer 10.1109/LCOMM.2018.2854879

The existing work mainly assumes that the activity of PU is

slotted, e.g., the state of PU maintains unchanged during one

slot, and varies only from one slot to another slot [2], [4].

However, in practice, the spectrum occupation of PU may

arrive or depart at an arbitrary time, and this assumption

inevitably causes the capacity performance degradation, espe-

cially in CR systems with highly dynamic spectrum occupation

by PU or long sensing duration of SU [5], since the actual

PU state is possibly not consistent with the sensed PU state

under such an assumption. Lu et al. [6] and MacDonald and

Popescu [7], consider the effect of non-slotted PU’s state

on the average capacity in HD CR systems. It makes more

sense to take the non-slotted PU state into account in FD CR

systems, since in such systems the overall slot is used for

spectrum sensing [8], which means that the state of PU

may change during the sensing duration in a much higher

probability.

In this letter, the capacity of FD CR systems with the non-

slotted PU state change is analyzed by establishing a novel

four-state Markov model based on different combination of

PU and SU states, and then is maximized by proposing a near-

optimal algorithm based on gradient descent. To the best of

our knowledge, there is little work considering the effect of

non-slotted PU activity on FD CR systems. Cheng et al. [8]

and He et al. [9] analyze the sensing performance in FD CR

systems under non-slotted PU state. However, the change of

PU state is not considered, i.e., “idle” and “busy” states of

PU are analyzed individually. Moreover, the authors do not

consider the effect of action taken in the previous slot by the

SU on the current slot. However, whether the self-interference

is present or not should depend on the sensing result in the

previous slot.

II. S

YSTEM MODEL

An FD CR system including one PU pair and one SU pair is

considered, where the spectrum is licensed to the PU pair, and

the SU pair is allowed to access the spectrum only when there

is a spectrum hole based on the overlay paradigm in an FD

manner, i.e., the SU antennas perform spectrum sensing and

data transmission simultaneously [2]. The state of PU spectrum

occupation is modeled as a non-slotted and dynamic binary

process, i.e., the state of PU switches between ON and OFF

at arbitrary time point and holds in a random duration. It is

assumed that the durations of PU pair’s occupancy and absence

are both exponentially distributed with means λ and τ,where

λ and τ denote the average number of samples corresponding

to PU pair’s occupancy and absence, respectively, and can be

practically set based on the PU activity measurements and

See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

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