Wireless Personal Communications Systems – CSE5807 Lecture: 07 Stephen Giles and Satha K. Sathananthan School of Computer Science and Software Engineering Monash University Australia These slides contain figures from Stallings, and are based on a set developed by Tom Fronckowiak .

Locating a WLAN Service Set Identifier (SSID): Beacons: Unique, case sensitive, alphanumeric value from 2-32 characters long. Used as a network name. Sent in beacons, probe requests, probe responses and other types of frames. Beacons: To organize and synchronize wireless communications. From AP to station in infrastructure mode. From station to station in ad hoc mode. Provide functions including Time synchronization FH or DS parameters SSID information Traffic Indication Map Supported rates

Locating a WLAN Scanning: Passive Scanning Active Scanning Process of listening for beacons on each channel for a specific period of time. Continuing process even after association. Active Scanning Sending of probe request frame by a wireless station when it seeks a network to join. The probe request frame contains either a particular network’s SSID or broadcast SSID.

Authentication Wireless client’s identity is verified by the network/access point. Access Point => Accept/Deny Authentication Methods: Open System Authentication Based on SSID only. Option of using WEP for only encrypting data. Shared Key Authentication Use WEP. AP LAN Authentication Request Frame Authentication Response Frame

Association Allowed to pass data through access point => “Associated”. Authentication => Association Wireless client can authenticate more than one access point at a time but can associate only one access point. AP LAN Association Request Frame Association Response Frame

Roaming AP Wireless client determines based on the signal strength. Disassociation Frame Reassociation Frame Wireless client determines based on the signal strength. IEEE802.11 does not define how should be performed. But some basic building blocks for this process. Active and passive scanning, reassociation process. New IEEE802.11f standard for roaming. Inter Access Point Protocol (IAPP).

Load Balancing A B Multi-cell structure with co-located access points creating a common coverage area. Wireless clients automatically associate with the access point that is less loaded and provides the best signal quality.

Adaptive Rate Selection (ARS) 11 Mbps 2 Mbps Speed adjustment with varying distance and interference. Switched between specified data rates. Important in planning: Network throughput Cell sizes Power outputs of access points and wireless clients Security

Power Management Continuous Aware Mode: Power Save Polling (PSP): Uses full power and no sleep mode. Wireless client determines based on the signal strength. Power Save Polling (PSP): Wireless client powers down for a very short amount of time. In BSS, traffic indication map (TIM) is used to notify buffered traffic. In ad hoc, “Ad hoc traffic indication messages” are used to notify buffered traffic.

IEEE802.11 Physical Layer MAC PLCP MAC Management PHY LLC PMD Data Link Layer Physical Layer MAC PLCP MAC Management PHY LLC PMD Management Physical Layer Convergence Protocol (PLCP): Responsible for carrier sensing assessment and forming packets for different physical layers. Physical Medium Dependent (PMD) protocol: Defines modulation and coding technique for signaling. Physical Layer Management: Decides on channel tuning to different options for each physical layer.

IEEE802.11 Standards IEEE802.11 IEEE802.11b IEEE802.11a IEEE802.11g Frequency 2.4GHz 5GHz Max. Rate 2Mbps 11Mbps 54Mbps Modulation FHSS DSSS OFDM

IEEE802.11 Physical Layer: FHSS SYNC (80) SFD (16) PLW (12) PSF (4) CRC (16) Whitened MPDU (<4096 Bytes) PLCP (always 1Mbps) 1 or 2 Mbps) Preamble Header MPDU: MAC Protocol Data Unit SYNC: Alternating 0 and 1 SFD: Start of Frame Delimiter – specific pattern of 16 bits (0000110010111101) PLW: Packet Length Width PSF: Packet Signaling Field CRC: Cyclic Redundancy Check – to protect the PLCP bits

IEEE802.11 Physical Layer: FHSS SYNC (80) SFD (16) PLW (12) PSF (4) CRC (16) Whitened MPDU (<4096 Bytes) PLCP (always 1Mbps) 1 or 2 Mbps) Preamble Header FHSS PMD hops over 78 channels of 1 MHz in the center of the 2.44 GHz ISM bands. Modulation: Gaussian Frequency Shift Keying (GFSK) 1Mbps – Two levels of GFSK 2Mbps – Four levels of GFSK Three patterns of 26 hops => Selection by PHY Management layer. 0, 3, 6, 9,……75 1, 4, 7, 10, …..76 2, 5, 8, 11, …..77 Minimum hop rate 2.5 hops per second. Maximum transmitted power is 100mW.

IEEE802.11 Physical Layer: DSSS SYNC (128) SFD (16) Signal (8) Service (8) Length (16) FCS (8) MPDU PLCP (always 1Mbps) 1 or 2 Mbps) Preamble Header MPDU: MAC Protocol Data Unit SYNC: Alternating 0 and 1 SFD: Start of Frame Delimiter – specific pattern of 16 bits (1111001110100000) Signal: Data rate Service : Reserved for future use Length: Length of MPDU in microsecond FCS: PLCP header coding

IEEE802.11 Physical Layer: DSSS SYNC (128) SFD (16) Signal (8) Service (8) Length (16) FCS (8) MPDU PLCP (always 1Mbps) 1 or 2 Mbps) Preamble Header Barker code of length 11. Uses non-overlapping pulses at chip rate of 11Mcps occupying 26 MHz. Modulation: 1Mbps => DBPSK 2Mbps => DQPSK ISM band at 2.4 GHz divided into 11 overlapping channels spaced by 5 MHz. Maximum transmit power is 100mW.

IEEE802.11b Physical Layer Defines a new coding, Complementary Code Keying (CCK) to support data rates of 5.5 Mbps and 11Mbps. 1Mbps => Barker Code and DBPSK 2Mbps => Barker Code and DQPSK 5.5Mbps => CCK and DQPSK 11 Mbps => CCK and DQPSK Uses the same PLCP as the IEEE802.11 DSSS standard. Interoperates with IEEE802.11 networks.

IEEE802.11a Physical Layer Based on OFDM scheme. Operates at 5 GHz UNII bands. Eight non-overlapping channels of 20 MHz at the two lower bands of the 5 GHz UNII band. Each channel is divided into 52 subcarreirs, each approximately 300 kHz. Data is transmitted in parallel on each subcarrier. Forward Error Correction (FEC) codes are used to correct errors. Data rates: 6, 9, 12, 18, 24, 36, 48 and 54 Modulation: BPSK, QPSK, 16-QAM and 64-QAM

IEEE802.11g Physical Layer Based on OFDM scheme. Operates at 2.4 GHz ISM bands. Backward compatibility with IEEE802.11b. Switch automatically to CCK/Other modulations. Data rates: 1, 2, 5.5, 6, 9, 11, 12, 18, 22, 24, 33, 36, 48 and 54 Mbps. Use optional CCK-OFDM.

IEEE802.11a and HiperLAN-2 IEEE802.11a HiperLAN-2 Frequency 5 GHz Max. trans. Rate 54 Mbps Medium Access Through sensing Centralized scheduling QoS support PCF ATM/802.1p/RSVP Wired backbone Ethernet Ethernet/ATM/ UMTS/PPP/IP Connectivity Connectionless Connection-oriented

Wireless LAN: Deployment Requirements: - Facility (Building plan). - Applications. - Users. - End user devices. - Battery longevity. - Coverage areas. - Security. Design: - System Architecture. - Identifying standards. - Selecting devices. Installation and Testing.

Wireless LAN: Deployment RF interference (from other devices). Interoperability issues (eg.: IEEE 802.11 a & IEEE 802.b). Security holes. Application interfaces/requirements. Unclear requirements.

Wireless LAN: Design Technical Considerations: Adequate radio coverage throughout the service area. Adequate capacity to handle traffic load. Network performance. Main design steps: Selection of AP locations. Assignment of radio frequencies to APs.

Wireless LAN: Design Radio propagation is mostly unpredictable. Design is iterative process. Steps involved: Initial selection of AP locations. Test and redesign. - Adjusting the AP locations based on signal strength measurements. Creation of coverage map. Assignment of frequencies (or channels) to APs. Signal strength measurements and minimizing co-channel coverage overlap.

WLAN Design: Access Points Based on measurements. Layout and construction of buildings determine the coverage area of each AP. Must avoid coverage gaps. Space APs as far apart as possible to minimize: - the cost of equipment and installations. - the co-channel overlap.

WLAN Design: Access Points R D

WLAN Design: Access Points R D

WLAN Design: Channel Allocations Once APs are located and their coverage areas are identified, radio channels are assigned to the APs. Radio channels are assigned in a way that provides the smallest possible co-channel overlap. In high-density areas: Multiple radio channels. Reducing the coverage areas of each APs. Coverage-oriented design: In low density areas, minimizing the number of APs. Capacity-oriented design: In high-density areas, assuring adequate capacity to serve all users.

Wireless Metropolitan Area Networks

Wireless Metropolitan Area Networks Defined in IEEE802.16 standard. Use licensed spectrum in 10 GHz – 66 GHz. Provide public network service to fee-paying customers. Use point-to-multipoint architecture with stationary rooftop or tower-mounted antennas. Provide efficient transport of heterogeneous traffic supporting quality of service (QoS). Are capable of broadband transmissions.

IEEE 802.16 Protocol Architecture

IEEE 802.16a Support to mesh network topology. Line of sight is not required. Also operates at frequencies between 2 and 11 GHz. Dynamic Frequency Selection (DFS) to avoid interference with WLAN. Further MAC and QoS support. Three radio technologies: Single carrier modulation format. OFDM OFDMA Centralized and distributed MAC mechanism.

Required Reading Reference W. Stallings, “Wireless Communications and Networks” Prentice-Hall, 2000. >> Chapter 13 & 14 Reference K. Pahlavan and K. Krishnamurthy “Principles of Wireless Networks”, Prentice-Hall, 2002.