Resource Allocation Call Admission Control Wireless Information Networking Group (WING) EEL 6591 Wireless Networks Resource Allocation Call Admission Control

Outline Resource allocation Call admission control FCA DCA HCA Wireless Information Networking Group (WING) Outline Resource allocation FCA DCA HCA Call admission control guard channel fractional guard channel queueing priority intelligent CAC

Resource Allocation Resource (channel) Wireless Information Networking Group (WING) Resource Allocation Resource (channel) frequency channels time slots codes Channel allocation (assignment): commonly used with the notion that each channel supports one service (voice dominated services) 1st and 2nd generation: channel allocation 3rd and 3+ generation: resource allocation one service may require multiple channels

Channel Allocation Fixed channel allocation (FCA) Wireless Information Networking Group (WING) Channel Allocation Fixed channel allocation (FCA) a fixed set of channels is allocated to a cell permanently simple but not adaptive to traffic condition Dynamic channel allocation (DCA) all channels are placed in a pool, are assigned to calls as needed complex but adaptive to network changes Hybrid channel allocation (HCA)

Wireless Information Networking Group (WING) FCA Ideally, if all service distribution and channel condition are uniform, then identical cells are used, each of which has the same number of channels assigned In practice, the non-uniform case, cell sizes and number of channels for each cell may be possible, optimization may be formulated heavily loaded cells are assigned more channels

Channel Borrowing Schemes Wireless Information Networking Group (WING) Channel Borrowing Schemes Can be FCA or DCA Static channel borrowing scheme (FCA) unused channels from lightly loaded cells are reassigned to heavily loaded cells channel locking: borrowing forbids the use of the same channel in other cells--frequency reuse distance Dynamic channel borrowing schemes deal with short-term allocation of borrowed channels: call-based or time-based or traffic based nominal cell vs donor cell

Channel Borrowing Schemes Wireless Information Networking Group (WING) Channel Borrowing Schemes Simple channel borrowing schemes any nominal channel can be borrowed by a neighboring cell for temporary use can be borrowed if induced interference does not affect the QoS for the ongoing calls better than FCA in terms of call blocking probability Choice of borrowing channels borrow from the richest: cell with most free channels basic algorithm: minimizes the future channel locking basic algorithm with reassignment: switch to nominal borrow first available: not to optimize but quick

Channel Borrowing Schemes Wireless Information Networking Group (WING) Channel Borrowing Schemes Hybrid channel borrow schemes (HCB) Simple HCB: two sets of channels, one is for borrowing, one is for nominal use only borrowing with channel ordering: same as simple HCB with variable the sizes of the two sets according to the traffic condition: ordering all channels from the best for nominal to the best for borrowing borrowing with directional channel locking: a channel is suitable for borrowing if it is also free in the three nearby co-channel cells channel assignment with borrowing and reassignment: minimizes the interference in a cluster

Dynamic Channel Allocation (DCA) Wireless Information Networking Group (WING) Dynamic Channel Allocation (DCA) Overcome temporal and spatial variation of traffic in cellular systems Main idea: evaluate the cost of using each candidate channel and select the one with the minimum cost provided that certain interference constraints are satisfied cost function: depends on future blocking probability in the vicinity of the cell (cluster), the usage frequency of the candidate channel, the reuse distance, channel occupancy distribution, radio channel measurements of individual mobile users, or the average blocking probability of the system

Dynamic Channel Allocation (DCA) Wireless Information Networking Group (WING) Dynamic Channel Allocation (DCA) Centralized DCA and distributed DCA Centralized DCA first available: not optimize but quick locally optimized dynamic assignment: minimize the cost function of blocking probability in the cluster channel reuse optimization schemes: maximize the efficiency of the system (the channel utilization of each channel) mean square: minimize the mean square of distance among the cells using the same channel nearest neighbor (NN): use an available channel occupied in the nearest cell in the allowable reuse distance (>=D) nearest neighbor plus one: NN+1-- (>=D+1) schemes with channel rearrangement

Dynamic Channel Allocation (DCA) Wireless Information Networking Group (WING) Dynamic Channel Allocation (DCA) Distributed DCA information of a cluster/block will be shared local packing DCA (LP-DCA): each BS assigns channels to calls using the augmented channel occupancy (ACO) matrix, which contains necessary and sufficient local information for the BS to make a decision (channel packing area: an area channel cannot be reused, channel assignment block-by-block or cluster-by-cluster) LP-DCA with adjacent channel interference (ACI) constraint

Dynamic Channel Allocation (DCA) Wireless Information Networking Group (WING) Dynamic Channel Allocation (DCA) Signal strength measurement-based distributed DCA: interference adaptation schemes using measurements sequential channel search: MS/BS pair examines channels in the same order and choose the first available with acceptable SIR minimum signal-to-noise interference ratio dynamic channel selection: each MS estimates the interference probability and selects the BS which minimizes its value channel segregation: scan all channels and selects a free channel with acceptable co-channel interference level Performance analysis simulation-based study need to create various scenarios for traffic distribution

Hybrid Channel Allocation (HCA) Wireless Information Networking Group (WING) Hybrid Channel Allocation (HCA) Simple approach channels are divided into two sets: one for fixed channel assignments, the other is for dynamic channel allocation adaptively adjust the sizes of those two sets of channels (moving boundary) HCA with channel reordering/rearrangement Flexible channel allocation light load: DCA heavy load: FCA Resource allocation: multiple channels allocation

Call Admission Control (CAC) Wireless Information Networking Group (WING) Call Admission Control (CAC) CAC decision for handling calls new calls handoff calls QoS-based calls predictive CAC combined design of resource reservation and CAC cell-based or cluster-based (shadow cluster concept)

CAC-Guard Channel Non-prioritized scheme (NPS) Guard channel scheme Wireless Information Networking Group (WING) CAC-Guard Channel Non-prioritized scheme (NPS) cell-based strategy a call is accepted if a free channel at BS is available Guard channel scheme C channels in a cell, C-m of them are reserved for handoff calls a handoff call is admitted if there is a free channel a new call is admitted if the number of busy channels is less than m, otherwise is rejected cutoff priority

CAC-Guard Channel Fractional guard channel scheme Wireless Information Networking Group (WING) CAC-Guard Channel Fractional guard channel scheme parameterization approach admission probabilities: b0, b1,.., bC, i.e., a new call is admitted with probability bj when there are j busy channels in the cell, while handoff calls are admitted if there is a free channel (bC=0) special cases guard channel: b0=b1=..=bm=1, bm+1=..=bC=0 parameters can be adaptively adjusted according to traffic situation

CAC-Guard Channel Performance analysis call blocking probability: p0 Wireless Information Networking Group (WING) CAC-Guard Channel Performance analysis call blocking probability: p0 forced-termination probability or handoff call blocking probability: pf arrival process: Poisson process new call arrival process: ln handoff call arrival process: lh channel holding time: m r = ln/m , rh = lh/ m

CAC-Guard Channel p(j): probability of j busy channels, then Wireless Information Networking Group (WING) CAC-Guard Channel p(j): probability of j busy channels, then

CAC-Guard Channel Blocking probabilities Wireless Information Networking Group (WING) CAC-Guard Channel Blocking probabilities

CAC-Guard Channel Fractional guard channel Wireless Information Networking Group (WING) CAC-Guard Channel Fractional guard channel

Call Dropping Probability Wireless Information Networking Group (WING) Call Dropping Probability Pd: probability that a call is prematurely terminated due to handoff failure (lack of resource in the target cell) Users are more sensitive to call dropping than to call blocking Pd=pf for wired networks: no handoff Can be measured: ratio of the number of calls dropped to the total number of new calls accepted Can be computed (see works by Fang et al)

CAC-Guard Channel Some thoughts Wireless Information Networking Group (WING) CAC-Guard Channel Some thoughts these assume Poisson assumption for call arrivals: handoff arrivals may destroy this assumption exponential assumption for channel holding time: not valid for many cases (verified by experimental data) new calls and handoff calls may have different average channel holding times: two-dimensional Markov model may be necessary! Fang and his colleagues investigate these issues extensively (see my papers and references therein) multi-dimensional Markov chain model

CAC-Queueing Schemes Queueing handoff calls Queueing new calls Wireless Information Networking Group (WING) CAC-Queueing Schemes Queueing handoff calls handoff requests are usually made earlier than what QoS needs at the old cell, hence can be queued so that handoff calls can gain higher priority over new calls two thresholds can be used for CAC: queueing & blocking predictive handoff scheme based on moving speed so that reservation request can be made measurement-based queueing: rank requests according to received power level or power change Queueing new calls suitable for delay insensitive new calls

Wireless Information Networking Group (WING) Intelligent CAC Requested resource may vary: multiple channels (amount) Shadow cluster concept CAC decision is based on a shadow cluster: a new call is accepted if the requested channel bandwidth in the cell and the corresponding amount in cells of the shadow cluster for reservation are enough need probability transition from a cell to its shadow cluster use information exchanged among all BSs in the shadow cluster

Intelligent CAC Reservation-based CAC Wireless Information Networking Group (WING) Intelligent CAC Reservation-based CAC each cell resource are divided into three parts used resource: Bused reserved resource: Bres (requested from neighboring cells) free resource: Bfree reservation strategy thresholding scheme: a resource request will be denied if a threshold for the sum of the used and the reserved resources exceeds a threshold CAC a new call is accepted if Bused+ Bres+Breq< Bc, where Bc is a resource threshold, Breq is the requested amount by the new call

Intelligent CAC Predictive CAC QoS prioritized schemes can be designed Wireless Information Networking Group (WING) Intelligent CAC Predictive CAC directional: measure or predict the moving direction and make reservation only in the vicinity of the direction moving speed/timing: predict the moving speed and estimate the time for handoff, allocate resource accordingly (may combine with reservation strategy) GPS position information: moving speed and direction can be made available QoS prioritized schemes can be designed some handoff calls may be less important than some new calls (data vs voice)

Reading Katzela and Naghshineh’s survey paper (1996) Wireless Information Networking Group (WING) Reading Katzela and Naghshineh’s survey paper (1996) Hong and Rappaport’s paper (1986) Levine, Akyildiz and Naghshineh’s paper (1997) My own papers (check with the instructor)