Jung-Sun Um

Applying Radio Environment Maps to Cognitive Wireless Regional Area Networks

The IEEE 802.22 wireless regional area network (WRAN) is the first worldwide commercial application of cognitive radio (CR) networks refarming the TV broadcast bands. According to US FCCs recent public notice, WRAN products are scheduled to be available for the market by February, 2009. This paper first presents a brief review of the IEEE 802.22 WRAN standardization, and then introduces the radio environment map (REM) as an innovative cost-efficient approach to developing and managing WRAN systems. REMs can provide powerful infrastructure support to the functionality of the WRAN cognitive engine (CE). The data model of the REM is presented together with an extensive discussion on how to exploit the REM for a variety of applications in WRAN systems, focusing on the REM-enabled case- and knowledge-based learning algorithms (REM-CKL) for WRAN CEs. Furthermore, REM-based radio scenario-driven testing (REM-SDT) is also presented as a viable approach to evaluating the performance of CEs. Future research topics are discussed in the final section.

Development of Radio Environment Map Enabled Case- and Knowledge-Based Learning Algorithms for IEEE 802.22 WRAN Cognitive Engines

The IEEE 802.22 wireless regional area network (WRAN) is the first worldwide commercial application of cognitive radio (CR) networks in unlicensed television broadcast bands. With the intent of efficiently occupying under-utilized spectrum, the network must be cognizant of spectrum available for secondary use and vacate channels as primary users are present. According to FCCs recent public notice, WRAN products are anticipated to be available for the market by February, 2009. This paper first presents a generic architecture for WRAN cognitive engines (CE), and details the design of a CE leveraging the radio environment map database and case-and knowledge-based learning algorithms (REM-CKL). Furthermore, the performance of REM-CKL CE has been evaluated under various radio scenarios and compared to search-based optimizers, including a genetic algorithm (GA). The simulated results show that the WRAN CE can make significantly faster adaptations and achieve near-optimal utility by synergistically leveraging REM-CKL and a local search (LS). Insights into REM-CKL, GA, and LS CE have been gained through the WRAN CE testbed development and preliminary testing.

Cognitive Radio test-bed based on ECMA-392 International Standard

Cognitive Radio (CR) technology is one of the promising technology to efficiently utilize the unused radio spectrum. Recently, the Federal Communications Commission (FCC) allowed TV white space (TVWS) to be used for data communications provided the licensed user operations should be protected. The FCC made the rules and regulation for using the TVWS. Till now there is no real deployment of any communication system that operates on TVWS. As the first step towards the deployment of a communication system that operates on TVWS, we developed a UHF band CR test-bed based on ECMA-392 international standard. ECMA-392 standard defines the MAC and PHY for operation in TVWS for communication between portable devices. In this paper, we present the design and implementation of our test-bed system in detail. We also verified that the test-bed system operates in lines with the FCC rules.

Throughput Performance Optimization of Super Dense Wireless Networks With the Renewal Access Protocol

As a promising solution for handling super dense wireless networks, wireless local area networks (WLANs) have been intensively considered due to their wide availability. However, the contention-based MAC protocol in WLANs should be modified because of its inefficiency. To this end, we consider a recently proposed novel MAC protocol called the renewal access protocol (RAP). With the RAP, we analyze two strategies for resolving collisions efficiently and achieving optimal throughput performance in super dense WLANs: strategies without and with grouping. First, we analyze the asymptotic behavior of the RAP itself (i.e., without grouping) as the number of terminals goes to infinity. We show that the RAP can achieve optimal throughput even in super dense WLANs and the relevant optimal access probability can be derived in a closed form. Second, we propose a grouping strategy in the RAP called the grouped RAP (G-RAP). While a grouping strategy in the IEEE 802.11ah standard is based on time division, our G-RAP is based on transmission attempts. So the G-RAP does not waste channel resources. We show that the G-RAP achieves the optimal network throughput for any group structure if terminals use the optimal access probability that we derive. Our analytical results are validated by simulation.

Adaptive Resource Allocation for OFDMA with Mixed Frame Structure

This paper introduces a reconfigurable mixed frame structure and a resource allocation algorithm for OFDMA systems supporting both the band-AMC and diversity modes in the frame. To reduce the total feedback without significant performance loss, we assign a user to the diversity subchannel when the band-AMC mode has no gain over the diversity mode based on the frequency selectivity of the user. After user selection, we apply joint power and rate allocation to exploit the asymmetry in required transmit power of the band-AMC mode and the diversity mode. The results reveal that the mixed frame with simple user classification provides a performance comparable to the frame with band-AMC mode only at a much reduced feedback. In particular, it is observed that the mixed frame with frequency division is preferable to that with time division by increasing the throughput of the users at the cell boundary in a large cell.

Optimal throughput analysis of a super dense wireless network with the Renewal Access Protocol

As Wireless Local Area Networks (WLANs) become denser and denser recently, the contention-based MAC protocol such as the IEEE 802.11 DCF, the de facto standard for the WLAN, should be modified to handle such dense WLANs. To this end, we consider a recently proposed novel MAC protocol called the Renewal Access Protocol (RAP) in this paper. With the RAP, we consider two strategies for resolving collisions efficiently and achieving high throughput performance in a super dense WLAN: strategies without and with grouping. First, we analyze the asymptotic behavior of the RAP itself (i.e., without grouping) as the number of terminals goes to infinity. We show that the RAP can achieve optimal throughput even in a super dense WLAN and the related optimal access probability of the RAP can be derived in a closed-form from the analysis. Second, we propose a new grouping strategy in the RAP and call it the grouped RAP (G-RAP). While a grouping strategy in the IEEE 802.11ah standard is based on time division, which can cause a waste of channel, our grouping strategy is based on transmission attempts, which does not waste channel resources. From the analysis we show that the G-RAP easily achieves the optimal network throughput performance for any group structure (i.e., unform group size and arbitrary group size) if terminals use the optimal access probability that we derive. Our analytical results are validated by simulation.

Development and performance improvement of cognitive radio testbed on TV white space

Cognitive radio technologies have been studied for enhancing various aspects of wireless communication in terms of optimization of system parameters or dynamic spectrum access. Recently, testbed implementations have been frequently introduced to verify the feasibilities of these researches. The possibility on sharing TV bands with an unlicensed service is also proved by several platforms for data communication using TV white space. In this paper, we introduce a cognitive radio testbed which can improve the system capacity by using carrier aggregation functionality or 2×2 MIMO on the UHF TV bands. Detailed design and implementation issues focused on carrier aggregation are described. Finally, operating scenario and performance evaluation of our testbed are demonstrated.

Multi-antenna-based transmission strategy in 5 GHz unlicensed band

Spectrum sharing technology has received a lot of attention as a promising solution for the problem on the shortage of spectrum resources due to mobile traffic increase. For the purpose of coexistence without harmful interference to incumbent services, secondary users (SUs) in spectrum sharing systems should adjust their transmission power while complying with regulatory requirements. In this paper, we develop the transmission strategies for multiple-antenna-based SU devices in 5GHz unlicensed band where a radar system is allocated as a primary user. We analyze the achievable throughput and bit error performances for the SU receiver using zero-forcing linear processing under imperfect channel estimation. Given the analytic results, we propose the dynamic transmission strategy on determination of the optimal number of active transmit antennas according to the restricted maximum transmission power corresponding to the received radar signal strength.

Analysis of channel access mechanism on 5 GHz unlicensed band

Data offloading on unlicensed band is one of the significant solutions in the era of the mobile traffic explosion. To utilize spectrum resource on unlicensed band, it is required to fairly coexist with other devices which are operating in the same channel. It can be achieved all secondary users to comply with channel access mechanism. In this paper, we analyze the frame based and load based channel access mechanism for 5 GHz unlicensed band defined by European regulatory domain. Numerical and simulation results are provided to validate our analysis.

A design approach of radio frequency module for TV white space based on filter bank

This paper presents a design scheme of radio frequency (RF) module using filter bank in order to operate the overall TV broadcast band (470 MHz ~ 698 MHz). To this end, several band pass filters (BPFs) with a relatively sharp skirt characteristic are employed for compliance with TV white space (TVWS) regulations. Performance test results show that the error vector magnitude (EVM) of the implemented RF transmitting chain is less than 1.5 %. The noise figure (NF) of the RF receiving chain is measured to be 6.0 dB. From the results, the proposed RF module can be adequately utilized for TV white space applications.