Yabin Ye

Outage probability analysis for cognitive radio network caused by primary users

Cognitive radio systems offer the opportunity to improve spectrum utilization while avoiding the interference to primary users. On the one hand, secondary users must be aware of the interference caused to primary users. Therefore, cognitive radio network should control their transmission power. On the other hand, the interference from primary network may degrade the performance of cognitive network. This paper considers the outage probability of cognitive radio network coexisting with primary users. A closed-form outage probability is derived for cognitive network with two nodes. The outage probability is mainly determined by the interference from primary users.

OFDM Subcarriers Coding for Enhancing Spectrum Notch

Because of its flexible spectrum shaping, OFDM technologies can be used for cognitive radio as signaling method. Spectrum notches can be generated through turning off subcarriers to protect primary users (licensee users), but the intercarrier interference may limit the notch depth. This paper focuses on the enhancing methods to deepen spectrum notch and proposes two kinds of OFDM subcarriers coding methods. These methods can deepen spectrum notch efficiently without causing much system complexity. They also have respective advantages that can be applied to different situations.

Spectrum-aware Location-based Routing in Cognitive UWB network

Cognitive ultra-wideband (UWB) network is the UWB network with the ability of sensing spectrum, detecting the available spectrum holes in primary system, and communicate in the detected spectrum holes. Based on the precise position capability of UWB technology and the spectrum sensing information, local clusters are constructed by neighbor nodes which operated in the same spectrum channel, and the entire network is interconnected by the clusters through bridge gateway nodes. Furthermore, a spectrum-aware routing scheme is provided for clustered cognitive UWB network, which including the process of routing discovery and repairing. The unique feature of this routing scheme is its ability of intelligent adaptation to the change of network and available spectrum resource. Simulation proved the performance of spectrum-aware routing in dynamic spectrum environment is better than traditional routing scheme with fixed spectrum allocation.

Capacity analysis of cognitive UWB networks

The integration of cognitive radio and Ultra wideband (UWB) networks had attracted lots of research interests. Cognitive UWB networks not only provide very high data rates but also guarantee the uninterrupted communication of primary system operated in the same frequency band. In this work the problem of analyzing the capacity of cognitive UWB networks is investigated. Taking into account of several factors such as transmission power constraints, interference temperature constraint in the receiver of primary system, outage probability and maximum allowed users are calculated by semi-analytical approach. Simulations are provided to illustrate the analysis. It is also proved that the increase of interference temperature will deteriorate the capacity of cognitive UWB network; however the constraint of interference temperature is related to the constraint of transmission power.

A Novel Active Spectrum Sensing Scheme for Cognitive MB-OFDM UWB Radio

Spectrum awareness is the key technique for Cognitive Radio (CR). A special spectrum sensing scheme is necessary for Cognitive UWB radio (CUWB) because of its lower radio power and ultra wide bandwidth. Although CUWB transmitter and receiver could respectively detect the spectrum holes, they couldnt communicate with each other probably if they are out of the communication range or there isnt common usable spectrum segment for them. No sensing technique deals with these problems properly. In this paper a novel active spectrum sensing scheme for cognitive MB-OFDM UWB radio is presented to settle the above problems. The scheme takes full advantage of UWB and finds usable channels directly for CUWB transmitter and receiver through sending beacon signals and acknowledgement signals. This active spectrum sensing scheme is totally different from existing sensing methods and has its own advantages.

The Tradeoff between Channel Capacity and Out-of-Band Interference of Cognitive Radios

Two points need to be considered on power loading policy of cognitive radio (CR) systems. The first is to maximize the channel capacity over the given frequency band, which is detected usable for CR systems. The second is the out-of-band interference suppression of the CR systems. In the paper based on the mathematical expression of the interference power caused by MB-OFDM based CR systems, the relationship of the symbols on the sub-carriers can be obtained. To realize the relationship the sub-carrier weighting method can be adopted. With the effect of the weighting factors, the symbols relationship can be satisfied, and simultaneously the maximum channel capacity can be achieved on certain degree. The simulation results of the relationship among the three parameters, channel capacity, interference power and total transmission power, also shows that a better tradeoff can be achieved between the channel capacity and the interference power.

Peak-to-Average Power Ratio Analysis of PCC-OFDM Signals

In this paper, a statistical analysis of the peak-to- average power ratio (PAPR) of Polynomial cancellation coded OFDM (PCC-OFDM) signals is presented. PCC-OFDM has the good performance of compressing intercarrier interference (ICI) at the cost of high PAPR. The most PAPR analysis assume the subcarriers to be identically and independently distributed (i.i.d). However, the correlation between adjacent pairwise subcarriers of PCC-OFDM causes the assumption not valid. The adjacent partial transmit sequence (PTS) with parameter constraints can be used to reduce the PAPR of PCC-OFDM. The simulation results show that the theoretic analysis is very close to experimental results. The PAPR of PCC-OFDM signals with 128 subcarriers exhibit near 2dB higher than the same type normal OFDM. PTS based method proposed in this paper can reduce the PAPR of PCC-OFDM to the normal complex-value OFDM level while keeping PCC relation.

Architecture for Next-Generation Reconfigurable Wireless Networks using Cognitive Radio

The next generation of wireless networks, as envisioned by recent advances in cognitive radio (CR) technologies, will be intelligently adjust their configuration to changes in the communication environment. Reconfigurability is set to be an important facet in the evolving world of mobile and wireless communications, through which technologies such as cognitive radio are greatly facilitated. In next generation of reconfigurable wireless networks, various wireless access networks coexist in the same frequency band using cognitive radio and internetworking using IP multimedia subsystem (IMS). This paper therefore discusses the introduction of a system architecture that incorporates cognitive radio and IMS. The architecture takes the emerging 3GPP system and Wimax system as an example, and focuses on the issue of common signaling, resource management and security.

The Constraints Satisfied to Suppress the Interferences Caused by MB-OFDM UWB Based Cognitive Radio Systems; One Type of Low Density Parity Check(LDPC)-like Modulation Scheme

A mathematical expression of side-band interferences caused by sub-carriers of multi-band (MB)-OFDM UWB based cognitive radio is derived. Based on this expression, the constraint relationship among transmitted symbols, which is satisfied to suppress the interferences, is obtained. Combined with this constraint, the design process of a type of LDPC-like modulation scheme is described. With modulation schemes of this type, the bit rate error (BER) performance of MB-OFDM UWB based cognitive radio systems is improved, and simultaneously, the side-band signals decrease more quickly. As a result, by the only measure of tuning off the sub-carriers at the corresponding position a deeper spectral notch can be generated. The interferences to other protected services are suppressed sufficiently and finally the coexistence is achieved between MB-OFDM UWB based cognitive radio system and other narrow band radio systems.