WiMAX (Worldwide Interoperability for Microwave Access)

over the shortest distance between the BS and the user antenna under LOS conditions. Over the maximum distance of 50 kilometers under LOS conditions, or the maximum distance of 9 kilometers under NLOS conditions, throughput drops considerably. The transmission rate is symmetrical, i.e., the same for the uplink (upstream), i.e., the link from the remote terminal back to the BS, as for the downlink (downstream). The sole exception to this symmetry is in the case of full-featured CPE at the cell edge, where uplink transmission rates are constrained by power limitations.

WiMAX employs orthogonal frequency division multiplexing (OFDM), which subdivides the spec-

trum into a number of independent, narrowband subcarriers, across which it sends the signal in parallel fashion.Through sub-channelization on the uplink,WiMAX concentrates signal power into fewer OFDM

subcarriers, thereby extending the reach of the system, mitigating the effects of physical obstructions in an NLOS environment and reducing CPE power consumption. Multiple-input multiple-output (MIMO)

antennas employ space/time coding to compensate for multipath fading over long loops. At the customer premises is an adaptive, passive array antenna known as a pizza box, as it is about the size and shape of a pizza box. Rate-adaptive modulation dynamically adjusts the signal modulation technique of each carrier to compensate for variations in signal quality at that carrier frequency. Reed-Solomon forward error correction (FEC) is employed to deal with issues of signal quality and automatic repeat request (ARQ) is employed to request retransmission of any remaining errored frames. 802.16 specifications include several multiplexing options. Frequency division duplex (FDD) supports both half-duplex (HDX) and full duplex (FDX) communications, and time division duplex (TDD) supports half-duplex (HDX), only.The 802.16

security protocol is built on enhancements to the privacy key management (PKM) developed for cable modem communications.The protocol uses X.509 digital certificates with Rivest-Shamir-Adleman (RSA) encryption for authentication and key exchange. Traffic encryption options are data encryption standard (DES) and advanced encryption standard (AES). 802.16 specifications include convergence sublayers designed for mapping services to and from 802.16 connections. The ATM convergence sublayer is for ATM services and the packet convergence sublayer is for packet services such as IPv4, IPv6, Ethernet, and Virtual LAN (VLAN).

WiMAX offers differential quality of service (QoS) based on four polling schedules:

• Unsolicited grant service (UGS) is designed for services such as T1 and E-1.

• Real-time polling service is designed for services such as voice over Internet Protocol (VoIP) and IP-based streaming audio and video.

• Non-real-time polling service is designed for services such as Internet access.

• Best effort service provides neither throughput nor latency guarantees.

See also 802.16, AES, ARQ, ATM, authentication, base station, broadband, BWA, cable modem, carrier, DES, digital certificate, E-1, EMI, encryption, Ethernet, ETSI, FDD, FDX, FEC, HDX, HiperMAN, IPv4, IPv6, latency, LOS, MIMO, modulation, narrowband, NLOS, OFDM, overhead, pizza box, PKM, protocol, rate adaption, Reed-Solomon, RFI, RSA, signal, subcarrier, T1, TDD, throughput, VLAN, VoIP, WiMAX Forum, and X.509.

• small and medium enterprise (SME)
• small business enterprise (SBE)
• Small Computer System Interface (SCSI)
• small office/home office (SOHO)
• SMDR (Station Message Detail Record)
• SMDS (Switched Multimegabit Data Service)
• SME
• Smell-O-Vision
• SMF (Single-Mode Fiber)
• SMF (Single-Mode Fiber)
• S/MIME (Secure Multipurpose Internet Mail Extension)
• S/MIME (Secure Multipurpose Internet Mail Extension)
• SMR (Specialized Mobile Radio)
• SMS
• SMSC (Short Message Service Center)
• SMTP (Simple Mail Transfer Protocol)
• SNAFU (Situation Normal All Fouled Up)
• SNAFU (Situation Normal All Fouled Up)
• SNA (Systems Network Architecture)
• SNMP (Simple Network Management Protocol)
• SNMP (Simple Network Management Protocol)
• SNR (Signal-to-Noise Ratio)
• SOA (Service-Oriented Architecture)
• social engineering
• socket