Bài giảng mạng không dây chương 8 wireless lans, mans and pans

Chương Wireless LANs, MANs and PANs Agenda • Introduction • Wireless Local Area Networks (WLANs) • Enhancement for IEEE 802.11 • • • Wireless Metropolitan Area Networks (WMANs) Wireless Personal Area Networks (WPANs) ZigBee 1/19/22 – Department of Computer introduction 1/19/22 – Department of Computer Introduction • WMAN, WLAN, WPAN provide wireless data connectivity, but with different characteristics and expectations and therefore different market segments – WMAN: cover an entire metropolitan area – WLAN: provides similar services but covers a much smaller area (e.g., a building, an office campus, lounges) WPAN: is an extremely short–range network, formed around the personal operating space 1/19/22of a user – Department of Computer – Introduction 1/19/22 – Department of Computer Wireless Local Area Networks (WLANs) 1/19/22 – Department of Computer IEEE 802.11 Standard • • • The IEEE group that proposed the standards for indoor LANs (e.g., Ethernet) The early 1980s published a standard for WLANs and named it the IEEE 802.11 (now known as IEEE 802.11a) Physical layer PHY use carrier frequency of 2.4GHz, MAC standard specifies with data rate of or Mbps These are just the standards for which a compatible product canof Computer be manufactured 1/19/22 – Department • IEEE 802.11 Standard • • Provide wireless network connection for fixed, portable, and moving stations within tens to hundreds of meters Major amendments: IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, and IEEE 802.11n; their most significant differences lie in the specification of the PHY layer 1/19/22 – Department of Computer IEEE 802.11 Amendments • IEEE 802.11a – Ratified in 1999 – Throughput up to 54Mbps – Unlicensed National Information Infrastructure (UNII) 5GHz freq band  less interference – Modulation: OFDM with 52 subcarriers spanning over a 20MHz spectrum Each subcarrier can be modulated with BPSK, QPSK, 16-QAM, or 64-QAM, depending on 1/19/22 – Department of Computer the wireless environment – IEEE 802.11 Amendments • IEEE 802.11b (known as Wifi) – August 1999 – 2.4 GHz ISM band, basic rate of 11 Mbps and a fall-back rate of 5.5 Mbps – Uses a direct extension of DSSS on the PHY layer 1/19/22 – Department of Computer 10 IEEE 802.15.4 Data Link Layer (DLL) The IEEE 802.15.4 MAC provides • services to an IEEE 802.2 type LLC through the service specific convergence sublayer (SSCS) • A proprietary LLC can access the MAC layer directly without going through the SSCS – Department of Computer 75 The SSCS ensures compatibility between •1/19/22 IEEE 802.15.4 Data Link Layer (DLL) The MAC sublayer provides • – MAC data service, through the MAC common part sublayer (MCPS–SAP) – MAC management services, through the MAC layer management entity (MLME–SAP) – These provide the interfaces between the SSCS (or another LLC) and the PHY layer – MAC management service has only 26 primitives as compared to the IEEE 802.15.1, which has 131 primitives and 32 events 1/19/22 – Department of Computer 76 IEEE 802.15.4 Data Link Layer (DLL) MAC frame structure • 1/19/22 – Department of Computer 77 IEEE 802.15.4 PHY Layer • • • Two PHY layer choices based on the DSSS: – 2.4 GHz ISM band, available worldwide – 868/915 MHz for Europe and the US, respectively Data rates supported – The ISM band PHY layer offers 250 kbps – The 868/915 MHz PHY layer offers 20 and 40 kbps The lower rate can be translated into better sensitivity and larger coverage area The higher rate means lower duty cycle, higher 1/19/22 – Department of Computer 78 IEEE 802.15.4 PHY Layer • Channel specs: – 868/915 MHz PHY • • • • 1/19/22 Supports a single channel between 868.0 and 868.6 MHz and 10 channels between 902.0 and 928.0 MHz Uses a simple DSSS where each bit is represented by a 15-chip maximal length sequence (m-sequence) Encoding is done by multiplying the m-sequence with + or − The resulting sequence is modulated by the carrier signal using BPSK – Department of Computer 79 IEEE 802.15.4 PHY Layer • Channel specs: – 2.4 GHz PHY – 16 channels between 2.4 GHz and 2.4835 GHz with MHz channel spacing – Uses a 16-ary quasi-orthogonal modulation technique based on DSSS – Binary data is grouped into 4-bit symbols, each specifying one of 16 nearly orthogonal 32-bit chip pseudo-noise (PN) sequences for transmission 1/19/22 – of Computer 80 PN sequences– Department for successive data symbols IEEE 802.15.4 PHY Layer • Channel specs: – In terms of energy conservation, orthogonal signaling performs better than differential BPSK – In terms of receiver sensitivity, the 868/915 MHz has a 6–8 dB advantage 1/19/22 – Department of Computer 81 PHY Layer Packet Structure • PHY packet fields: – Preamble (32 bits) synchronization – Start of packet delimiter (8 bits) signifies end of preamble – PHY header (8 bits) specifies length of PSDU – PSDU ( ≤ 127 bytes) PHY layer payload 1/19/22 – Department of Computer 82 zigbee 1/19/22 – Department of Computer 83 ZigBee vs Bluetooth 1/19/22 – Department of Computer 84 ZigBee vs Bluetooth • • ZigBee focuses on control and automation with a very low data rate, whereas Bluetooth focuses on connectivity between consumer electronics products with the intent of replacing cable connections Bluetooth requires a higher data rate and higher power consumption for transfering data 1/19/22 – Department of Computer 85 ZigBee vs Bluetooth • • In time-critical applications, ZigBee is designed to respond quickly Bluetooth takes much longer to respond, which could be detrimental in such applications Still, frequency hopping does provide inherent security in Bluetooth 1/19/22 – Department of Computer 86 ZigBee Specifications • • • Specially used in wireless sensor networks Aim: small batteries, requiring low bandwidth and low latency and low energy consumption for the long operational lifetimes of network devices Data rate – 250 Kbps in 2.4 GHz ISM band – 20 kbps in the 868 MHz band 1/19/22 – 40 Department Computer kbps in the– 915 MHzof band 87 ZigBee Specifications • • • The data transmission is very infrequent in ZigBee, making interference of very little concern MAC layer implementation is based on CSMA/CA The network layer is designed to implement topologies such as star, peer to peer, and clustered – All devices must have a short 16-bit, IEEE addressing, 1/19/22 – Department of Computer 88 ZigBee Specifications • • The application layer – Maintains the table of binding for matching two or more devices – Handles the discovery of devices operating in the same space – Assigns roles to each device and builds a secure network The manufacturer develops the actual application on top of the ZigBee standard 1/19/22 – Department of Computer 89 ... revisions – 2001: IEEE 80 2.16 (WiMAX) – Jan 2003: 80 2.16a – Q3 2004: 80 2.16REVd – 2005: 80 2.16e (Mobile WiMAX) – Jun 2009: 80 2.16j – 2011: 80 2.16m (WiMAX 2.0) – 2012: 80 2.16-2012 1/19/22 – Department... amendments: IEEE 80 2.11a, IEEE 80 2.11b, IEEE 80 2.11g, and IEEE 80 2.11n; their most significant differences lie in the specification of the PHY layer 1/19/22 – Department of Computer IEEE 80 2.11 Amendments...Agenda • Introduction • Wireless Local Area Networks (WLANs) • Enhancement for IEEE 80 2.11 • • • Wireless Metropolitan Area Networks (WMANs) Wireless Personal Area Networks (WPANs) ZigBee 1/19/22