Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

1. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities Cavalcanti, D. and Ghosh, M. Cognitive Radio Oriented Wireless Networks and Communications, 2008. (CrownComm 2008) Lecturer: Chang Han-Tien Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

2. Outline • Introduction • Regulatory Scenario • Overview of The 802.22 Standard • Spectrum Management Model • Conclusions • Comments Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

3. Introduction • Last-mile broadband access • different solutions may be more efficient for different applications and deployment regions • A successful deployment of wireless broadband in rural communities should consider • Coverage, Capacity, Installation and operational costs, Business models • WiFi network (IEEE 802.11) • design for short/medium range connectivity • solution for long-distance access [2] • Cellular system • the deployment cost is an issue for rural communities. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

4. Introduction (cont’d) • Cognitive Radio [4] • an intelligent wireless communication system that is aware of its environment (sensing spectrum) • uses the methodology of understanding-by-building to learn from the environment • adapt to statistical variations in the input stimuli • Two objectives • highly reliable communication whenever and wherever needed • efficient utilization of the radio spectrum Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

5. Introduction (cont’d) • IEEE 802.22 (WRANs) • operate in the TV spectrum band (54 MHz~862 MHz) as secondary users • under regulatory rules to avoid interference with the primary users (incumbent, TV broadcasting) • Key issues • Incumbent protection • Self-coexistence • Spectrum management Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

6. Regulatory Scenario • Cognitive radio networks • enable flexible, efficient and reliable spectrum • by adapting the radio’s operation characteristics to the real-time conditions of the environment • limited applicability under legacy spectrum usage • Command and control • Exclusive-use • New dynamic spectrum access models • In order to exploit the full capabilities of CRNs Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

7. Regulatory Scenario (cont’d)Dynamic spectrum access models • Shared-use of primary licensed spectrum • where secondary users share the spectrum with primary users on a non-interfering basis • Spectrum underlay • Limit the secondary users’ transmit power to very low level in order not to interfere with primary users • Spectrum overlay • Enable devices to operate in the spectrum white spaces • Implement reliable incumbent detection and frequency agility mechanisms Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

8. Regulatory Scenario (cont’d)Dynamic spectrum access models • Spectrum commons • the spectrum is shared under equal rights by all devices on an unlicensed basis in the model • Open-access model in ISM (2.4GHz) and I-NII (5 GHz) • Reduce the overcrowding condition in these unlicensed bands • IEEE 802.22 standard • shared-use spectrum model • protection of primary users while providing Quality of Service (QoS) for the secondary users. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

9. Regulatory Scenario (cont’d)Protection of Incumbents • Spectrum sensing is a key technology to detect incumbents in the TV bands. • Incumbent Detection Thresholds (IDT) • If an incumbent signal above the IDT is detected, the secondary system must react appropriately to avoid harmful interference. • The incumbent signal shall be detected with probability exceeding the Probability of Detection (PD) parameter • Probability of false alarm shall be equal or lower the the PFA parameter • Channel Detection Time (CDT) Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

10. Regulatory Scenario (cont’d)Protection of Incumbents • If an incumbent signal above the IDT • In the adjacent channels • apply transmit power control to avoid leakage in other channels • In the operating channel • vacate the channel within the Channel Move Time (CMT) • an aggregate transmission time equal to the Channel Closing Transmission Time when switch to backup channel Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

11. Regulatory Scenario (cont’d)Protection of Incumbents • PFA is important for the secondary systems’ QoS and efficient spectrum utilization [13] Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

12. Overview of the 802.22 standard • 802.22 WRAN is a point-to-multipoint system • Base station (BS) • Consumer Premise Equipments (CPEs) • equipped with a spectrum sensing module • meet the regulatory requirement of sensing • Expected coverage area is around 30 Km • Address markets in sparse populated areas Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

13. Overview of the 802.22 standard (cont’d)The 802.22 PHY • OFDMA multiple access • Data rate • 1.5 Mbit/s in the downstream (DS) • 384 Kbit/s in the upstream (US) • Support 255 CPEs per BS per TV channel (6MHz) Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

14. Overview of the 802.22 standard (cont’d)The 802.22 MAC • BS controls the access to wireless medium • take on-demand basis in the US direction • use TDM (Time Division Multiplexing) in the DS • New range of cognitive radio feature supports • Reliable incumbent detection • Frequency agility • Self-coexistence • the coexistence amongst 802.22 WRANs Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

15. Overview of the 802.22 standard - The 802.22 MAC(cont’d)Superframe and frame structures • Superframe consists of 16 frames • facilitate incumbent protection, synchronization, and self-coexistence • start with the superframe preamble, frame preamble, Superframe Control Header (SCH), and Frame Control Header (FCH) Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

16. Overview of the 802.22 standard - The 802.22 MAC(cont’d)Superframe and frame structures • Frame is divided into DS and US sub-frames • DS/US MAPs and channel descriptor broadcast messages (DCD and UCD) • Option in the US sub-frame • be used for ranging, bandwidth request and Urgent Coexistence Situation (UCS) notification • Self-Coexistence Window (SCW) • For coexistence beacon transmissions at the end of US sub-frame Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

17. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

18. Overview of the 802.22 standard - The 802.22 MAC(cont’d)Incumbent Detection Support • Scheduling of network quiet periods (QPs) • avoid overlapping of data transmissions • BS schedules network QPs for sensing • suspend all the traffic in the cell, let CPEs sample the channel for detecting the incumbent • intra-frame and inter-frame quiet periods • minimize the impact of QPs on users’ QoS Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

19. Overview of the 802.22 standard - The 802.22 MAC(cont’d)Incumbent Detection Support • Channel measurement management • In-band (i.e. in the operating channel and first adjacent channels) • scheduled by the BS during the QPs • Out-of-band (other channels that may be used as backup • may be done during the CPEs idle time • Occupied by other WRANs, should use the QPs schedule Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

20. Overview of the 802.22 standard - The 802.22 MAC(cont’d)Incumbent Detection Support • Notification phase • advertising the QP scheduling in the SCH • channel quiet request message (CHQ-REQ) to stop traffic within its cell • bulk measurement request message (BLM-REQ) to request CPEs to perform measurements • the result are reported back in bulk measurement reply message (BLM-REP) Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

21. Overview of the 802.22 standard - The 802.22 MAC(cont’d)Incumbent Detection Support • a CPE detected the presence of incumbent • use the UCS notification slots to inform BS • the notification transmitted using a contention-based or CDMA-based • BS combines the information from various CPEs • React more efficiently in timely manner Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

22. Overview of the 802.22 standard - The 802.22 MAC(cont’d)Frequency Agility • An incumbent is detected on the operating channel (N) or adjacent channels (N-1,N+1) • BS triggers a switch to a backup channel • Maintain a list of back channels • Challenge: a seamless channel transition • Two channel management mode • Implicit mode (DCD Broadcast message) • Don’t require extra management messages • Explicit mode (CHS-REQ, Channel switch request) • Provides greater flexibility in different granularities • To single CPE or to a group of CPEs (multicast message) Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

23. Overview of the 802.22 standard - The 802.22 MAC(cont’d)Self-coexistence • Synchronize the QPs among neighboring cells, in order to reduce the overall QPs • Synchronize the superframes using positioning satellite capabilities at the BSs • Exchange their QP schedule through the SCH as well as the Coexistence Beacon Protocol • use SCW to allow CPEs (BSs) to exchange coexistence beacons (QP schedule’s information) • Each BS should select CPEs to transmit CBP packets according a periodic schedule, and it should also select CPEs to listen for CBP packets Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

24. Overview of the 802.22 standard - The 802.22 MAC(cont’d)Self-coexistence • When a CPE receives a CBP packet from a neighboring cell • Forward to the information to its BS • Exchange information amongst neighboring cells • Efficient spectrum sharing • Using the intelligent scheduling mechanism • Dynamic resource renting/offering • On-demand spectrum contention Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

25. Spectrum Management Model • Spectrum Manager • a central entity collocated with the WRAN BS • taking the key decisions and triggering the proper events/actions (central intelligence) • a part of the MAC layer management entity • Spectrum Automaton • act as a slave to the SM • control the local CPE’s spectrum sensing function as requested by the BS’s SM Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

26. Spectrum Management Model (cont’d) • Spectrum Manager’s main functions • 1. Maintain spectrum availability information; • 2. Channel classification and selection; • 3. Association control; • 4. Trigger frequency agility related actions; • 5. Manage mechanisms for self-coexistence. • Geo-location module • acquire precise positioning and time synchronization information Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

27. Spectrum Management Model (cont’d) Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

28. Overview of the 802.22 standard - The 802.22 MAC(cont’d)Superframe and frame structures • Collaborative spectrum sensing and incumbent database • Aggregating information from other sources • Make decisions based on spectrum sensing information only when the incumbent database isn’t available • Frequency agility actions • Switch the entire cell to a new operating channel; • Direct a single CPE or a group of CPEs to a different operating channel; • Terminate operation in a given channel for a single CPE, a group of CPEs or the entire cell; • Inform CPEs of channels status updates Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

29. Conclusions • The shared usage model with primary users can be realized with existing cognitive radio technologies • Enable new opportunities for wireless broadband access • Protection of incumbents and achieve efficient spectrum utilization • Future work • Optimized scheduling algorithms • Channel selection and intelligent scheduling algorithm • Collaborative sensing techniques • System level evaluation to assess the robustness of 802.22 Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

30. Comments • It’ important to find the balance point between the incumbent protection and the secondary user’s QoS • The importance of spectral resources • Need more improvements for the 802.22 draft Cognitive Radio Network: Enabling New Wireless Broadband Opportunities