Broadband wireless access technology provides high-speed network connections to static locations that are so complete that there is a standard for second-generation wireless metropolitan area networks (MANs). The IEEE 802.16 standard with WirlessMAN ™ space interface sets the scope for widespread and effective worldwide deployment. This article is from the article by Carl Eklund, Roger B. Marks, Kenneth L. Stanwood and Stanley Wang published in the journal IEEE Communications. This article outlines the MAC specification and the physical layer of this new standard. Introduction and market opportunities The IEEE 802.16-2001 standard was completed in October 2001 and was published on April 8, 2002, defining the WirelessMAN ™ space interface specification for metropolitan networks. Completion of Broadband Wireless Broadband Acceptance Prevention as a key new tool in trying to link buildings and business entities to the world's core telecommunications networks. As defined in the IEEE 802.16 standard, a wireless metropolitan network that provides network access to buildings via an outdoor antenna can communicate with the central radio station (BS). Because wireless systems are geared toward large, desolate geographic regions without the need to develop costly infrastructure such as in the deployment of cable connections, technology is less expensive to develop. and thus leading to increased broadband access everywhere. The MAC WirelessMAN design can adapt every connection with perfect QoS. With technology expanding in this direction, it is a standard developed to support those who always need mobility (such as in cars). The IEEE 802.16 standard was designed to open a set of air interfaces based on a common MAC protocol but with physical layer specifications depending on usage and spectral adjustments. concerned. Targeting frequencies from 10 to 66 GHz, where wide spectrum is available for global use, at which short wavelengths are considered as deployment challenges. For that reason, a revised project called IEEE 802.16a was completed in November 2002 and was released in April 2003. This standard is extended to support spatial interfaces for frequencies in the 2-11 GHz frequency band, including both licensed and unlicensed spectrum. Compared to higher frequencies, such spectra provide the opportunity to acquire more customers at an acceptable cost, although the data rates are not high. However, the services will target individual buildings or small and medium enterprises. Technology design issues MAC (Medium Access Control) The IEEE 802.16 MAC protocol is designed for point-to-multipoint wireless access applications. It directs to the need for very high bit rates, both uplink (to BS) and downlink (from BS). Bandwidth access and positioning algorithms must accommodate hundreds of endpoints per channel, with endpoints shared by multiple end users. Services that are required by these end-users remain the same as they are and include legacy time-division multiplexing, IP (Internet Protocol) and VoIP (packet over IP) packets. chemistry In order to support the diversity of services, 802.16 MAC must regulate both continuous and non-continuous traffic. At the same time, these services are waiting to be assigned quality of service (QoS) appropriate to such traffic patterns. MAC 802.16 provides a broad range of service types that are similar to traditional ATM services as well as newer services such as the guaranteed frame rate (GFR). The 802.16 MAC protocol must also support a variety of return requirements, including ATM protocol and packet-based protocols. Through features such as payload headers, encapsulation and fragmentation, converged subsets and MACs work together to deliver a much more efficient flow than the inherent transport mechanism. . The "request-grant" mechanism is designed to be highly variable, highly efficient, and self-correcting. In addition to basic tasks such as bandwidth allocation and data transport, the MAC includes a separate subclass that provides network access authentication and connection establishment to prevent service theft. It provides key exchange and encryption for separate data. Physical layer (PHY, physical layer) 10 - 66 GHz: In the design of the PHY specification for 10-66 GHz, "line-of-sight" propagation is necessary. Because of the "point-to-multipoint" architecture, the BS essentially transmits a TDM signal to individual subscriber stations that periodically locate the time slots. Upstream access by TDMA. Following extensive discussions of duplexing, a burst design was chosen that allowed both TDD (timedivision duplexing), where uplink and downlink were sharing the same channel but not simultaneous transmission and FDD (frequency-division duplexing). ) where the uplink and downlink operate in separate channels. This burst design allows both TDD and FDD to be processed in the same way. Options in both TDD and FDD support adaptive "bursts", where modulation and encoding options can be assigned on a per-burst basis. 2-11 GHz: Licensed and exempted bands are in the IEEE 802.16a project. The 802.16a standard mainly includes the development of new physical layer specifications for the spatial interface and each of them specifies the interoperability. The 2-11 GHz physical layer is designed for demanding non-line-of-sight (NLOS) operations. Since residential applications, propagation has to be done in multiple directions. In addition, outdoor antennas are expensive due to their high hardware and installation costs. Details about physical layer (PHY) PHY specification is defined for 10-66 GHz using burst single burst modulation with adaptive burst-profile, where transmission parameters, including modulation and coding schemes, can be Customized for each subscriber station (SS) on a single frame basis. Figure 1: Downlink subframe FEC (forward error correction) has the ability to change block size and error correction. This FEC is associated with an internal block encoder for smooth transmission of critical data, such as frame access and startup access. The system uses a 0.5, 1 or 2 ms frame. This frame is divided into physical slots for the purpose of allocating and recognizing the bandwidth of the PHY transitions. A physical slot is defined for four quadrature amplitude modulation (QAM) symbols. In the TDD scheme of the PHY, the sub-frame of the next uplink of the downlink in the same carrier frequency. In the FDD scenario, the sub-frames of the uplink and downlink eventually coincide, but they are carried on separate frequencies. The sub-frame of the downlink is depicted in Figure 1. The downstream subframe begins with a frame containing the DL-MAP framework for the current downlink frame as well as the UL-MAP for the specified time frame in the future. The downstream frame contains a TDM-portion immediately after the frame snippet. Downlink data is transmitted to each SS using a burst-profile agreement. In systems, after the TDM segment is a TDMA segment containing an extra preamble at the starting point of each new burst-profile. This feature allows better support for semi-duplex SSs. In a well-designed FDD system with multiple half-duplex SSs, some may transmit earlier in the frame than they receive. Because of their semi-duplex nature, these SSs lose synchronization with the downlink. TDMA-preamble allows them to regain that synchronization. Picture 2: The frame structure of the path A typical up-linking frame path for PHY 10-66 GHz is depicted in Figure 2. Unlike the downlink, UL-MAP grants resolution to specific SSs. The SS transmitters in the allocation region are assigned using burst-profile specified by the UIUC (Uplink Interval Usage Code) in the UL-MAP entry entry band for them. The upstream frame may also contain competitive-based positioning for early system access and "broadcast" or "multicast" bandwidth requirements. Access opportunities for system initialization are initially defined to be large enough to allow extra time to protect SSs that have not been resolved to the required transfer time to compensate for round- trip delay) for BS. Between PHY and MAC is a converged transmission layer (TC). This layer implements protocol variable length PDUs that can be changed into fixed length FEC blocks (plus a shortened block at the end) of each burst. . The TC layer has a size PDU that matches the current FEC block. It starts with a pointer indicating where the next MAC PDU entry starts inside the FEC block. See Figure 3. Figure 3: TC-PDU format The TC PDU allows the subsequent MAC PDU to be synchronized in the event that the previous FEC block has unrecoverable errors. Without a TC class, an SS or BS receiver will lose the entire rest of a burst when an irreparable fault occurs. Details about MAC (medium access control) MAC includes specialized subsets of service interfaces with higher layers, above the common core MAC subsystem, performing core MAC functions. Underneath the subclass are common subclasses (privacy sublayer). These subclasses converge on the service The IEEE 802.16 standard defines two specialized service aggregation subsets for mapping services to and from 802.16 MAC connections. The ATM aggregate child layer is defined for ATM services and the packet-class subsystem defined to map packet services such as IPv4, IPv6, Ethernet, and VLANs (virtual local area networks). The primary task of the subclass is to classify the service data units (SDUs) according to the appropriate MAC connection, preserve or enable QoS, and enable bandwidth allocation. In addition to these basic functions, converged subsets can also perform more complex functions such as blocking and rebuilding the payload header to improve airlink performance. ). Common part of sublayer Overview and overall architecture - In general, MAC 802.16 is designed to support point-to-multipoint architecture with a centrally controlled multiple-controller BS. On the way down, data to SSs is channeled in TDM mode. Uplinks are shared between SSs in the TDMA fashion. MAC 802.16 is connection-oriented. All services that include non-connectionless services are inherently mapped to a connection. That provides a mechanism for bandwidth requirements, the incorporation of QoS and traffic parameters, transport and routing of data to the appropriate convergence layer, and all other related activities. contract terms of service. Connections are referenced to 16-bit (16-bit connection identifier) CIDs and may require sequential bandwidth allocated or bandwidth required. Each SS has a standard 48-bit MAC address, but these serve primarily as a device identifier, since the root addresses used during the operation are CIDs. At the network level, the SS is assigned three management connections for each direction. These three connections reflect three different QoS requirements used by three different management levels. The first connection is a basic connection used to transmit short messages, "time-critical MAC" and RLC (radio link control). Primary management connection is used to transmit longer, more bearable messages than what is used to authenticate and set up the connection. Secondary management connections are used to transmit standards-based management messages such as DHCP (Dynamic Host Configuration Protocol), TFTP (Trivial File Transfer Protocol), and Simple Network Management Protocol (SNMP). In addition to these management connections, SSs are allocated transport connections for contracted services. Single-way transport connections simplify uplink and downlink QoS parameters and flow parameters. The MAC also stores additional connections for other purposes such as competitive initial start, broadcast downlink, and polling ). The MAC-PDU-MAC transmission of the IEEE 802.16 MAC supports different higher layer protocols such as ATM or IP. New MAC-SDUs coming from corresponding converged subsets are formatted in the MAC-PDU format, possibly with fragmentation and / or encapsulation, before being coupled through one or more connections to the MAC-PDU. agree the MAC protocol. After overcoming the airlink, the MAC-PDUs are structured back to the original MAC-SDUs, thus modifying the formatting implemented by the MAC layer protocol is "transparent" with receiving entity. IEEE 802.16 takes advantage of the integration of packaged and fragmented processes with bandwidth positioning to optimize both flexibility and performance. Fragmentation is the process by which a MAC-SDU is segmented into one or more MAC-SDU segments. Packaging is a process in which multiple MAC-SDUs are integrated into a MAC-PDU payload. Both processes can be started by a BS for a downlink connection or an SS for an uplink connection. IEEE 802.16 allows for fragmentation and simultaneous encapsulation so that bandwidth can be efficiently utilized. PHY support and frame structure - MAC IEEE 802.16 supports both TDD and FDD. In FDD, the "continuous" and "burst" are all supported. The "continuous" downlink takes into account performance enhancement techniques such as "interleaving." The "burst" (or FDD or TDD) route allows for more capacity-enhancing and capacity-enhancing technologies such as subscriber-level burst-profiling and improved antenna systems. The MAC builds the subframe of the downlink starting with a frame control that contains the DL-MAP and UL-MAP messages. They indicate the downlink PHYs as well as the bandwidth and burst-profile locations in the uplink. Figure 4: Minimum time between reception and UL-MAP application for an FDD system DL-MAP can always be applied to the current frame and always have at least two FEC blocks. The first PHY transition is expressed in the first FEC block, allowing for adaptive processing time. In both TDD and FDD systems, the UL-MAP provides initial positioning no later than the next downlink frame. However, the UL-MAP can locate the start of the current frame as long as the processing times and round-trip delays are monitored. The minimum time between the receipt and applicability of UL-MAP for an FDD system is shown in Figure 4. Radio Link Control - The improved technology of PHY 802.16 requires enhanced RLC, especially the PHY ability to transition from one burst-profile to another burst-profile. RLC must control this capability as well as traditional RLC functions. More details on RLC can be found in the original document. Uplink Scheduling Services - Each uplinked connection is mapped to a scheduling-service. Each scheduling-service involves a set of rules based on the BS scheduler responsible for allocating capacity for uplink and on-demand allocations between SS and BS. A detailed description of the rules and scheduling-service used for a particular uplink connection is negotiated at the connection setup time. Voluntary UGS (unsolicited grant service) services are transformed to provide services that create periodic fixed data units. When used with the UGS, the allocation subset includes the poll-me bit (see "Bandwidth requirements and allocation") as well as the slip indicator flag allowing the SS to report that the item Wait for propagation due to factors such as loss of allocation or deviation between IEEE 802.16 and external network. BS, thanks to the slip indicator flag, can allocate some additional capacity to the SS, allowing it to restore the average queue state. Connections configured with UGS are not permitted to use random access opportunities for requests. Bandwidth and allocation requirements - IEEE 802.16 MAC governs two layers of the SS, which are distinguished by their ability to accept bandwidth allocations for a connection or for SS integrity. Both SS bandwidth classes require bandwidth for each connection to allow the "BS uplink scheduling" algorithm to properly consider QoS when determining bandwidth. With allocation for each connection layer (grant per connection, GPC) of the SS, the bandwidth is allocated for a connection and the SS only uses this allocation for that connection. RLCs and other management protocols use bandwidth allocated to these management connections. With the allocation layer for each SS (grant per SS, GPSS), SSs are allocated bandwidths that are aggregated into a single grant for the SS itself. GPSS-SS should be smarter in handling its service quality. It will use the bandwidth specification for the requested connection, but not necessary. For example, if the QoS situation at SS has changed from the last request, SS has the option to send higher QoS data along with a bandwidth substitution request that is "stolen" from a lower QoS connection. . SS can also use some bandwidth to respond quickly so that changes in environmental conditions can be altered by sending, for example, a DBPC-REQ message. To bypass the normal sequential check routine, any SS with a connection running UGS can use the poll-bit in the allocation manager subkey to let the BS know it needs to be checked sequentially. Bandwidth requirements on another connection. BSs can only choose to store strips through sequential checks of SSs that voluntarily allocate services only if they have set a poll-me bit. Channel Acquisition - The MAC protocol includes an initialization procedure designed to eliminate the need for manual configuration. At the time of installation, an SS begins scanning its frequency list to find an active channel. It can be programmed to register with a specified BS, referencing a broadcast BS ID (programmable). This feature is useful for deploying where the SS can "hear" a secondary BS due to selective muffling or when the SS captures a "sidelobe" of an adjacent BS antenna. After deciding on which channel, the SS tries to synchronize the downlink by detecting the periodic frame preambles. Once the physical layer is synchronized, the SS searches for periodic UDC and DCD broadcast announcements that allow the SS to recognize the modulation and FEC schemes used on the carrier. SS Authentication - Each SS contains an X.509 certificate that is installed from the factory and the manufacturer's certificate. These certificates establish a link between the 48-bit MAC address of the SS and the shared RSA key, sent to the BS from the SS in the request for authorization and authentication information. The network is able to verify the similarity of the SS by examining the certificates and then checking the SS permissions. If the SS is authorized to join the network, the BS will respond to its request with an Authorization Reply containing an AK key encrypted with the SS shared key and used to Protect transactions later. During successful licensing, the SS will register with the network. That will establish a secondary management connection of the SS and identify the capabilities related to connection settings and MAC operation. The IP version used with the secondary management connection is also defined during registration. IP Connection - After registration, the SS wins an IP address via DHCP and sets the time of day via the Internet Time Protocol (ITP). The DHCP server also provides the address of the Trivial File Transfer Protocol (TFTP) server, from which the SS can request a configuration file. This file provides a standard interface that provides vendor-specific configuration information. Connection Settings - In general, the installation of service streams in IEEE 802.16 is initiated by the BS during initialization of the SS. However, service flows may also be set by the BS or SS. Typically SS initiates service streams only if there is a dynamically connected connection as a switched virtual connection (SVC) from an ATM network. Establishment of service flows is accomplished through a "three-way handshaking" protocol that requires service flow setup to be met and the response is acknowledged. Security Associations - The IEEE 802.16 security protocol is based on the PKM (Privacy Key Management) protocol, PKM is built around the concept of SAs (security associations). SA is a set of cryptographic methods and key combinations; That means, it contains information about which algorithms are applied, which keys are used, and so on. Each SS sets at least one SA during initialization. Each connection, with the exception of primary and primary management connections, is mapped to an SA or at the connection setup time or during operation. Epilogue The WirelessMAN ™ Spatial Interface offered in the IEEE 802.16 standard provides the foundation for the development and deployment of standards-based metropolitan area networks that provide broadband wireless access in a variety of regulatory environments. This standard is intended to take into account many suppliers that produce devices that can work together. However, it also focuses on different suppliers. For example, this standard provides a base station with a set of tools for effective planning. However, scheduling algorithms that determine overall performance will vary for different vendors and can optimize specific traffic patterns. In this way, the burst-profile characteristics allow for control to optimize the performance of PHY transport. Innovative vendors will introduce smart implementation plans to increase this opportunity while preserving their interoperability with compatible subscriber stations. The announcement of the IEEE 802.16 standard has an importance in which broadband wireless access goes to the second generation and initiates the establishment as an alternative trend for broadband access. Through the service of many volunteers, the IEEE 802.16 Working Group has succeeded in designing and creating a standard based on "forward-looking" technology. The IEEE 802.16 standard is the foundation of wireless metropolitan networks for the next few decades. Royal Union
