Service-Specific Convergence Sublayer(CS) : CS CID MAC CPS MAC
Common Part Sublayer(MAC CPS) : 802.16 MAC BS SS management QoS
ARQ(Automatic Repeat Request) Security Sublayer : BS SS Physical
Layer : OFDM FFT 5
QoS mechanisms Classification Mapping from MAC SDU fields (e.g
destination IP address) to CID and SFID Scheduling Downlink
scheduling module Simple, all queues in BS Uplink scheduling module
Queues are distributed among SSs. Queue states and QoS requirements
are obtained through BW requests. Algorithms not defined in
standard 9
Slide 10
IEEE 802.16 QoS Architecture 10
Slide 11
Service Types 11
Slide 12
Service Types (cont.) 12
Slide 13
Service Types (cont.) Extended rtPS (ErtPS) UGS rtPS Ex:
silence suppression VoIP BS UGS unicast grants SS ertPS BS QoS UGS
BS SS BS SS bandwidth stealing piggyback 13
Slide 14
Service Types (cont.) 14
Slide 15
Service Types (cont.) 15
Slide 16
Comparison Table QoS CategoryApplicationQoS Specifications UGS
Unsolicited Grant Service VoIP Maximum Sustained Rate Maximum
Latency Jitter Tolerance rtPS Real-Time Polling Service Streaming
Audio or Video Minimum Reserved Rate Maximum Sustained Rate Maximum
Latency Tolerate Traffic Priority ErtPS Extended Real-Time Polling
Service Voice with Activity Detection (VoIP) Minimum Reserved Rate
Maximum Sustained Rate Maximum Latency Tolerate Jitter Tolerance
Traffic Priority nrtPS Non-Real-Time Polling Service File Transfer
Protocol (FTP) Minimum Reserved Rate Maximum Sustained Rate Traffic
Priority BE Best-Effort Service Data Transfer, Web Browsing, etc.
Maximum Sustained Rate Traffic Priority priority 16
Slide 17
Poll/Grant Options in Scheduling Services Scheduling Type
Piggyback Request Bandwidth Stealing Polling UGSNot allowed PM bit
is used to request a unicast poll for bandwidth needs of non-UGS
connections. rtPSAllowed Scheduling only allows unicast polling.
nrtPSAllowed Scheduling may restrict a service flow to unicast
polling via the transmission/request policy; otherwise all forms of
polling are allowed. BEAllowed All forms of polling allowed.
ErtPSAllowed All forms of polling allowed 17
Bandwidth Management Bandwidth(BW) for a connection is
allocated on a demand assignment basis. Unused bandwidth allocation
will be withdrawn. Bandwidth is managed via Request/Grant Methods.
UGS services arent necessary to be requested,since the resource
needs are known in advance. Request can be used for all other
services. Bandwidth cant taken from a UGS service (its guaranteed)
while possible for other services. 19
Slide 20
Unicast polling Polled Request: polling sent from BS Unicast
polling Sent on SSs basic CID Transmission opportunities in Request
IE or Data Grant IE Data Grant IE can use a more efficient burst
file Request IE can only use the Request IE burst file(UIUC=1)
Unicast polling of an SS would normally be done by allocating a
Data Grant IE directed at its Basic CID The transmission of BRs is
contention-free 20
Slide 21
Unicast polling Unicast polling(cont.) 21
Slide 22
Multicast polling and broadcast polling Multicast polling and
broadcast polling Sent on multicast CID or broadcast CID Only the
members in the polled group will send BRs BRs are transmitted in a
contention way and the contention resolution algorithm is applied
BS shall individually poll the SSs periodically who dont have
bandwidth allocated With only one active UGS connection(BW stealing
and piggyback arent allowed), SS set PM bit asking BS to poll the
SS In case no enough bandwidth available for individual polling,
broadcast or multicast polling are used 22
Slide 23
Multicast polling and broadcast polling(cont.) Multicast and
broadcast polling 23
Slide 24
Bandwidth Stealing Bandwidth Stealing SS uses a portion of
allocated bandwidth for a connection for a connection to send
another bandwidth requests rather than sending data Not allowed for
UGS connection 24
Slide 25
Piggyback Request Piggyback Request The bandwidth request is
piggybacked onto a MAC PDU on an existing connection with allocated
bandwidth Not allowed for UGS connection The request is
unsuccessful if no grant has been received in next few UL-MAP
message 25
Slide 26
Bandwidth Allocation 802.16 MAC BS scheduler radio interface DL
UL requested bandwidth, QoS parameters available resources Grant
Per Subscriber Station (GPSS) BS SS Subscriber Station SS BS SS SS
26
Slide 27
Bandwidth Allocation (cont.) Downlink BS DL QoS BS scheduler SS
downlink burst(s) burst profile Uplink SS BS SS UL QoS (UGS, rtPS,
ertPS, nrtPS, and BE) BS UL unsolicited bandwidth grants piggyback
bandwidth request unicast polling (polling) contention-based
procedures (broadcast or multicast polling) 27
Transmission Scheduling Radio resources have to be scheduled
according to the QoS (Quality of Service) parameters Uplink
Scheduling the scheduling algorithms can be used : RR (Round Robin)
WRR (Weighted Round Robin) WFQ (Weighted Fair Queuing) WFFQ
(Worst-case Fair weighted Fair Queuing) VT (Virtual Time) DRR
(Deficit Round Robin) DDRR (Distributed Deficit Round Robin) EDF
(Earliest Deadline First) 30
Slide 31
WRR (Weighted Round Robin) The WRR algorithm is based on the
Round Robin algorithm but it takes into account the processing
capacity of each waiter. The administrators manually assign a
coefficient of performance to each waiter. ( 1, 2 and 3 in the
example). 31
Slide 32
WFQ (Weighted Fair Queuing) 32
Slide 33
EDF (Earliest Deadline First) A dynamic scheduling algorithm
used in real-time operating systems. It places processes in a
priority queue. Whenever a scheduling event occurs (task finishes,
new task released, etc.) the queue will be searched for the process
closest to its deadline. If there is a feasible schedule, then EDF
produces a feasible schedule 33
Slide 34
Scheduling Example Packet scheduling for QoS support in IEEE
802.16 broadband wireless access systems QoS WiMAX This scheduling
algorithm is proposed to assign: a fixed bandwidth for UGS, using
Earliest Deadline First (EDF) technique for rtPS, Weighted Fair
Queuing (WFQ) for nrtPS and equal distribution for BE. 34
Reference [1] IEEE Std 802.16-2009 [2] A. Ganz, Z.Ganz and
K.Wongthavarawat,Multimedia Wireless Networks: Technologies,
Standards, and QoS, Prentice Hall PTR, 2003, ch.7 [3] L. Nuaymi,
WiMAX: Technology for Broadband Wireless Access, Wiley, 2007, ch.11
[4] K. Wongthavarawat, and A. Ganz, Packet Scheduling for QoS
Support in IEEE 802.16 Broadband Wireless Access Systems,
International Journal of Communication Systems, Vol. 16, p81-96,
2003 [5] K. R. Raghu, S. K. Bose, and M. Ma, Queue Based Scheduling
for IEEE 802.16 Wireless Broadband, in Proc. 6th IEEE Int. Conf.
ICICS, 2007, pp. 15 [6] , , 2009 39