IEEE 802.16

1. IEEE 802.16

2. Topics • Introduction • Physical Layer • MAC Layer • QoS

3. Introduction • Physical Layer • MAC Layer • QoS

4. Goal: Provide high-speed Internet access to home and business subscribers, without wires. • Base stations (BS) can handle thousands of subscriber stations (SS) • Access control prevents collisions. • Supports • Legacy voice systems • Voice over IP • TCP/IP-Applications with different QoS requirements.

5. 802.16 standards: • 802.16.1 (10-66 GHz, line-of-sight, up to 134Mbit/s) • 802.16.2 (minimizing interference between coexisting WMANs.) • 802.16a (2-11 Ghz, Mesh, non-line-of- sigth) • 802.16b (5-6 Ghz) • 802.16c (detailed system profiles) • P802.16e (Mobile Wireless MAN)

7. Introduction • Physical Layer • MAC Layer • QoS

8. Adaptive Data Burst Profiles • Transmission parameters (e.g. modulation and FEC settings) can be modified on a frame-by-frame basis for each SS. • Profiles are identified by ”Interval Usage Code” (Downlink Interval Usage Code (DIUC) and Uplink Interval Usage Code (UIUC).)

9. Using both • TDM (Time Division Multiplexing) and • TDMA (Time Division Multiple Access) • What is the difference, you ask.. • TDM: Time-Division Multiplexing (TDM) is a type of digital or (rarely) analog multiplexing in which two or more signals or bit streams are transferred apparently simultaneously as sub-channels in one communication channel, but physically are taking turns on the channel. The time domain is divided into several recurrent timeslots of fixed length, one for each sub-channel. • TDMA: Time division multiple access (TDMA) is a channel access method for shared medium (usually radio) networks. It allows several users to share the same frequency channel by dividing the signal into different timeslots. The users transmit in rapid succession, one after the other, each using his own timeslot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only the part of its bandwidth they require. TDMA is used in the digital 2G cellular systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones.

10. The main difference between tdm and tdma (also fdm/fdma, etc) is that with tdm (also fdm, etc.) the signals multiplexed (i.e. sharing a resource) come from the same node, whereas for tdma (also fdm, etc.) the signals multiplexed come from different sources/transmitters.

11. Time Division Multiplexing (TDM) imply partitioning the bandwidth of the channel connecting two nodes into finite set of time slots.

12. Time Division multiple Access (TDMA) imply partitioning the bandwidth of a channel shared by many nodes, typically an infrastructure node and several mobile nodes, where each node gets to access its dedicated time slot.

13. Introduction • Physical Layer • MAC Layer • QoS

14. Connection orienteded • Connection ID (CID), Service Flows(FS) • Channel access: • UL-MAP • Defines uplink channel access • Defines uplink data burst profiles • DL-MAP • Defines downlink data burst profiles • UL-MAP and DL-MAP are both transmitted in the beginning of each downlink subframe (FDD and TDD).

15. TDD Downlink subframe

16. FDD Downlink subframe

17. FDD burst framing

18. Uplink subframe

19. Upplink periods • Initial Maintenance opportunities • Ranging • To determine network delay and to request power or profile changes. • Collisions may occur in this interval • Request opportunities • SSs request bandwith in response to polling from BS. • Collisions may occur in this interval aswell. • Data grants period • SSs transmit data bursts in the intervals granted by the BS. • Transition gaps between data intervals for synchronization purposes.

20. Bandwidth request and allocation • SubscribersStations may request bw in 3 ways: • Use the ”contention request opportunities” interval upon being polled by the BS (multicast or broadcast poll). • Send a standalone MAC message called ”BW request” in an allready granted slot. • Piggyback a BW request message on a data packet.

21. BS grants/allocates bandwidth in one of two modes: • Grant Per Subscriber Station (GPSS) • Grant Per Connection (GPC) • Decision based on requested bw and QoS requirements vs available resources. • Grants are realized through the UL-MAP.

22. Unicast Polling • BS allocates space for the SS in the uplink subframe. • SS uses the allocated space to send a bw request. • BS allocates the requested space for the SS (if available). • SS uses allocated space to send data. BS SS Poll(UL-MAP) Request Alloc(UL-MAP) Data

23. 4 types of Scheduling Service • Unsolicited Grant Service (UGS) • Real-time, periodic fixed size packets (e.g. T1 or VoIP) • Restrictions on bw requests (Poll-Me bit) • Slip Indicator (SI) • Real-Time Polling Service (rtPS) • Real-time, periodic variable sizes packets (e.g MPEG) • BS issues periodic unicast polls. • Cannot use contention requests, but piggybacking is ok. • Non-Real-Time Polling Service (nrtPS) • Variable sized packets with loose delay requirements (e.g. FTP) • BS issues unicast polls regularly (not necessarily periodic). • Can also use contention requests and piggybacking. • Best Effort Service • Never polled individually • Can use contention requests and piggybacking

24. Scheduling types

25. Introduction • Physical Layer • MAC Layer • QoS

26. The 802.16 standard specifies two modes for sharing the wireless medium: • point-to-multipoint (PMP) and • mesh(optional).

27. PMP: With PMP, the BS serves a set of SSs within the same antenna sector in a broadcast manner, with all SSs receiving the same transmission from the BS. Transmissions from SSs are directed to and centrally coordinated by the BS. • Mesh: Traffic can be routed through other SSs and can occur directly among SSs. Access coordination is distributed among the SSs.

28. PMP MODE • uplink (from SS to BS) and downlink (fromBS to SS) data transmissions occur in separate time frames. • In the downlink sub-frame, the BS transmits a burst of MAC protocol data units (PDUs). • In the uplink sub-frame, on the other hand, any SS transmits a burst of MAC PDUs to the BS in a time-division multiple access (TDMA) manner.

30. Downlink and uplink sub-frames are duplexed using one of the following techniques, as shown in above figure: • Frequency-division duplex(FDD) is where downlink and uplink sub-frames occur simultaneously on separate frequencies, and time-division duplex (TDD) is where downlink and uplink sub-frames occur at different times and usually share the same frequency. SSs can be either full duplex (i.e., they can transmit and receive simultaneously)or half-duplex (i.e., they can transmit and receive at nonoverlapping time intervals).

32. The MAC protocol is connection-oriented: all data communications, for both transport and control, are in the context of a unidirectional connection. • At the start of each frame, the BS schedules the uplink and downlink grants in order to meet the negotiated QoS requirements. • Each SS learns the boundaries of its allocation within the current uplink sub-frame by decoding the UL-MAP message. • The DL-MAP message contains the timetable of the downlink grants in the forthcoming downlink sub-frame. More specifically, downlink grants directed to SSs with the same DIUC are advertised by the DL-MAP as a single burst. Both maps are transmitted by the BS at the beginning of each downlink sub-frame. • Above Figure 2 shows the blueprint of the functional entities for QoS support, which logically reside within the MAC layer of the BS and SSs. • Each downlink connection has a packet queue (or queue, for short) at the BS (represented with solid lines). • In accordance with the set of QoS parameters and the status of the queues, the BS downlink scheduler selects from the downlink queues,on a frame basis, the next service data units (SDUs) to be transmitted to SSs.