IEEE C802.16m-08/1046
http://ieee802.org/16
An Nguyen
DHS/NCS
An.P.Nguyen@dhs.gov
The document describes prioritized QoS framework in network entry used to support the priority access in 802.16m
.
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IEEE C802.16m-08/1046
Priority access is one of important requirements of Emergency Telecommunications Service (ETS) [1]. ETS is a telecommunications service to facilitate emergency recovery operations for restoring the community infrastructure and for returning the population to normal living conditions after serious disasters and events, such as floods, earthquakes, hurricanes, and terrorist attacks. The ETS will be provided through shared resources from the public telecommunications infrastructure, which includes wireline, wireless, satellite, broadband cable, and any hybrid networks. ETS traffic needs to access, traverse, and egress these networks. Voice, video and data services are supported by ETS.
IEEE 802.16m has requirements on priority for the government and public safety. In Section 5.8 of IEEE 802.16m-07/002r4, it said
“IEEE 802.16m shall be able to support public safety first responders, military and emergency services such as call-prioritization, preemption, push-to-talk”. Priority access is also a SPWG requirement in Mobile WiMAX [2]. In Release 1.5, “R-[193] The
WIMAX network SHALL provide high priority for special circumstances such as emergency services and deadlock situations. Such high priority SHALL be protected with appropriate additional levels of authentication.” Priority access is required for National
Security and Emergency Preparedness (NS/EP) users.
In this contribution, we propose prioritized QoS framework in network entry to be considered by 802.16m.
The major purpose of this document is to propose prioritized QoS framework in network entry used to support the priority access in
802.16m. All the identified prioritized QoS framework in network entry is our recommendations to be included in 802.16m SDD.
Section 2 presents prioritized QoS framework in network entry to support priority access to be considered by 802.16m
Section 3 presents more detailed ETS requirements, especially in the area of priority access.
To support priority access in 802.16m, the following procedures are required
• User subscription
• Service priority invocation (service priority indication)
• User authentication (user identity; verifies the service indication is from priority user)
• Service authorization (specifies the service privileges of priority user)
• Service priority treatment (service differentiation)

IEEE C802.16m-08/1046
This document discusses the techniques used for service priority treatment. To provide service priority treatment using 802.16m networks, the following techniques are required:
• Prioritized network entry (initial ranging)
• Prioritized (initial) service flow setup and admission
• Prioritized session setup and maintenance
• Prioritized bandwidth request for admitted service flow
• Prioritized handover
The congestion points for radio access occur at contention-based and allocation-based transmission (shown in Figure 1). The contention-based transmission is mainly used for initial ranging and bandwidth request. The allocation-based is to allocate OFDMA capacity. This contribution discusses the prioritized QoS framework to support priority access for contention based transmission, specially in network entry.
16e MS
16m MS
16m MS
R1
R1
R1
ASN
16m BS
R6
R6
16m BS
ASN Gateway
• Initial ranging
• Bandwidth request
• Service flow admission
Figure 1: Radio Access Congestion Points
.
The protocol functions for priority access are shown in Figure 2. The priority access capability is supported by different logic entities in the MAC Common Part Sublayer. Network Entry Management entity is responsible for priority access to the contention resource such as initial ranging. Connection Management entity is responsible for service flow setup between BS and MS. And scheduler is for dynamic radio bandwidth allocation. All these entities shall coordinate with Radio Resource Management entity about the resource availability. Local Radio Resource stores local radio bandwidth utilization. Radio Resource Management is the entity to access and update the real-time radio resource information.
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IEEE C802.16m-08/1046
16m MS
Application Layer
MAC
Convergence Sublayer
Common Part Sublayer
Network
Entry
Management Local Radio
Resource
Radio
Resource
Management
Connection
Management
R1
16m BS
Application Layer
MAC
Convergence Sublayer
Common Part Sublayer
Network Entry
Management
Connection
Management
Local Radio Resource
Radio Resource
Management
Scheduler
Scheduler
Security Sublayer Security Sublayer
PHY PHY
Figure 2: 802.16m Protocol Functions for Priority Access
The 802.16e has the following network entry steps:
• Scanning
• Obtaining parameters
• Initial ranging
• Exchanging capabilities
• Authentication
• Registration
• IP connectivity
• Creating transport connection ( Adding service, service flow admission )
• Bandwidth Request for admitted service flow
The priority treatments for initial ranging, creating transport connection and bandwidth request steps are discussed in the following sections.
2.2.1 Introduction
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In IEEE 802.16e, initial ranging and bandwidth request use contention-based scheme to access the network. Initial ranging is for a new mobile station (MS) to join the network which requires a long preamble. The bandwidth request is for a MS to request uplink
(UL) allocation which requires a short preamble. The non-real time polling service (nrtPS) (for FTP) and best effort (for web browsing) use bandwidth request via contention-based or by piggybacking the requests to granted data allocations [3].
Initial ranging and bandwidth request adopt PN code sequences to mitigate collisions. The code is spread over multiple subchannels in one symbol. The minimal allocation for initial ranging is 6 adjacent subchannels and 2 symbols (also called UL initial ranging slot). The minimal allocation for bandwidth request is 6 adjacent subchannels and one symbol. The above definitions follow those in the WiMAX Forum Mobile System Profile. There are 144 tones in 6 subchannels. Since each tone is BPSK modulated, a PN code sequence for initial ranging and bandwidth request is 144 bits [3]. The number of codes is 256 in one sector, and these 256 codes are shared among initial ranging, periodic ranging, bandwidth request, and handover ranging. The collision detection is when a
MS does not get the expected response in a given time. The resolution is to use a truncated binary exponential backoff window.
There are few concerns of the 802.16e contention-based messaging protocols. First, based on the WiBro deployments, their capacity is actually the bottleneck of the network. Second, configurations for initial ranging and bandwidth request can be specified only on a per sector basis, i.e., they cannot be defined on a per user class per sector basis. As a result, no service differentiation can be provided to MSs for initial ranging or bandwidth request within a sector. We propose to have the parameters for initial ranging and bandwidth request to be specified on a per user class per sector basis for IEEE 802.16m. In this paper, we analyze the performance of prioritized initial ranging and illustrate its benefits using the Mobile WiMAX System Simulator [4].
2.2.2 Simulation Configurations
2.2.2.1 802.16e Initial Ranging Configuration
As previously described, the basic allocation for contention-based signaling is that two symbols are needed for initial ranging slot
(since the UL synchronization has not been achieved yet) and one symbol is for bandwidth request [5]. In the current IEEE 802.16
Rev2/D6, for the OFDMA PHY, after completion of contention-based initial ranging during network entry, BS shall send a CDMA allocation IE to MS. The CDMA allocation IE corresponds to a particular CDMA initial ranging code. After the MS receives the
CDMA allocation IE, the MS sends a RNG-REQ containing MAC address using UL resource pointed by CDMA_Allocation_IE.
When BS receives the RNG-REQ message, it shall respond with a RNG-RSP (with matching MAC address) message. The RNG-
RSP contains the CIDs (Basic & Primary Management) correspond with MAC address of the MS. If RNG-RSP message is lost, T3 of MS will expire, and MS shall perform contention-based initial ranging again.
There are two reasons that a MS does not get RNG-RSP. One is code collision (i.e., multiple MSs choose the same code) and the other is excessive interference. Reference 5 indicated that 30 ranging codes per initial ranging slot can be received at the BS at the
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IEEE C802.16m-08/1046 same time without having excessive interference. However, when talking to WiMAX chip set vendor at the IEEE 802.16 standards meetings July 2008, only 3 or 4 codes can be received at the same time.
To support prioritized initial ranging, there are two proposals. One is to boost up the transmit power of the initial ranging code, and the other is to reserve certain codes (and their associated resources) for the priority users. The following analyzes the performance of the latter proposal.
Traffic assumptions:
Intel’s contribution [6] assumes 10 MHz/10 MHz FDD and 60 VoIP calls/MHz/sector. (The 802.16m System Requirement
Document [SRD] defines the VoIP capacity [active users/MHz/sector] to be > 30.) However, the traffic load for initial ranging is more than what is generated by the number of VoIP calls. For example, all the following scenarios generate initial ranging load.
The user powers on their 802.16 device and stays idle (idle users), the user attempts to initiate a connection (i.e., data, VoIP, video)
(active users) or National Security/Emergency Preparedness ( NS/EP) users need to access the network during emergency. Hence, the traffic load is much higher than the assumption of considering only VoIP load.
Instead of pin pointing a specific traffic load, we use a parametric approach to model the traffic load. That is to say that we analyze the performance of prioritized initial ranging under various traffic loads. We assume that among the sector load for initial ranging,
R% is for regular calls and P% is for priority calls, where R = 90 and P = 10 [7]. The initial ranging arrival follows Poisson distribution.
Parameters:

Initial ranging region: The time between initial ranging regions (1 – 8 frames)

Number of initial ranging codes (1 – 256)

Number of initial ranging slots (1 – 2)
Interference analysis:
Two types of code interference analysis are modeled:
1.
Multiple users choose the same code (code collision)
2.
Excessive interference at the receiver (code interference)

Code interference threshold (4 or 8)
Mitigation techniques:
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IEEE C802.16m-08/1046
We investigate the effectiveness of the following mitigation techniques using modeling and simulation. a.
Dedicated code

Orthogonal code; this solves the code collision, but does not resolve code interference. b.
Dedicated initial ranging slot

Dedicated subchannel (orthogonal frequency) and dedicated symbol (orthogonal time); this solves code interference. c.
Time between dedicated initial ranging regions

Dedicated frame (orthogonal time); this solves code interference.
2.2.2.2 Simulation Results
Simulation is conducted for the following cases.
Case
I.1
I.2
I.3
I.4
I.5
I.6
II.1
Regular
IR code range
1-64
1-72
1-64
1-72
1-32
1-36
1-64
Priority IR code range
65-72
N/A
65-72
N/A
33-36
N/A
65-72
Regular
IR slot number
1
1
1
1
1
1
1
Priority IR Time slot number between regular IR
1 region
(every n th frame)
1
N/A
1
N/A
1
1
1
1
1
Time between priority IR region
(every n th frame)
1
N/A
1
N/A
1
Code interference threshold
8
8
8
4
4
8
4
N/A
2
1
1
N/A
1
II.5
III.1
1-32
1-72
33-36
1-72
1
1
2
N/A
1
1, 2, 3,
4,5,6,7
1
8
8
4
In Case I.1, there is only one initial ranging slot, but regular and priority users have their dedicated codes. In Case I.2, there is only one initial ranging slot, but regular and priority users share the code space. As shown in Figure 3, Case I.1 performs worse than case
I.2 which means if there are no orthogonal resources in time and/or frequency (e.g. initial ranging slot) for priority users, division of code space does not help. The reason is that since the dominating interference factor is excessive interference, division of the code space does not provide any benefit.
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IEEE C802.16m-08/1046
Initial Raning Performance Analysis for 802.16e/m Networks
0.5
0.4
0.3
0.2
0.1
1
0.9
0.8
0.7
0.6
0
0 0.5
1 1.5
2 overall IR success rate (I.2) reg interference (I.1) cc pri to pri (I.1)
2.5
3 3.5
4 4.5
5
Total IR Arrival Rate (= l t where t = 5 ms) regular IR success rate (I.1) overall interference (I.2) cc pri to reg (I.1)
5.5
priority IR success rate (I.1) cc all to all (I.2) cc reg to pri (I.1)
6 6.5
7 pri interference (I.1) cc reg to reg (I.1)
7.5
8
Figure 3: Initial Ranging Performance for Cases I.1 and I.2
Cases I.3 and I.4 are similar to Cases I.1 and I.2 except the code interference threshold is increased from 4 to 8. However, the overall trend does not change (the performance curves are not shown here).
Cases I.5 and I.6 (shown in Figure 4) are similar to Cases I.3 and I.4 except that the code space for regular user and priority user is reduced by half. The overall trend is still the same as that in Figure 3. However, the dominating interference factor is a function of the initial ranging load. For smaller initial ranging load, the dominating interference factor is code collision; for high initial ranging load, the dominating interference factor is the code interference. The interference threshold determines at what traffic load the excessive interference becomes the dominating factor. Since service differentiation is more needed during high load, the code space division does not help these two cases either.
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IEEE C802.16m-08/1046
Initial Raning Performance Analysis for 802.16e/m Networks
0.5
0.4
0.3
0.2
0.1
1
0.9
0.8
0.7
0.6
0
0 0.5
1 1.5
2 regular IR success rate (I.5) reg interference (I.5) cc pri to pri (I.5)
2.5
3 3.5
4 4.5
5
Total IR Arrival Rate (= l t where t = 5 ms) overall IR success rate (I.6) overall interference (I.6) cc pri to reg (I.5)
5.5
priority IR success rate (I.5) cc all to all (I.6) cc reg to pri (I.5)
6 6.5
7 pri interference (I.5) cc reg to reg (I.5)
7.5
8
Figure 4: Initial Ranging Performance for Cases I.5 and I.6
Cases II.1 shows a different trend (see Figure 5). The probability of success for priority initial ranging can be maintained about 90% for all initial ranging arrival load. The reason is a dedicated initial ranging slot is allocated for priority users.
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IEEE C802.16m-08/1046
Initial Raning Performance Analysis for 802.16e/m Networks
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0 0.5
1 1.5
2 2.5
3 3.5
4 4.5
5
Total IR Arrival Rate (= l t where t = 5 ms) priority IR success rate (II.1) pri interference (II.1) regular IR success rate (II.1) cc reg to reg (II.1)
5.5
6 reg interference (II.1) cc pri to pri (II.1)
6.5
7 7.5
8
Figure 5: Initial Ranging Performance Analysis for Cases II.1
Case II.5 has a similar trend as Case II.1 (the performance curves are not shown here). The differences between Case II.5 and Case
II.1 are that the former has half of the codes and more relaxed code interference threshold.
Case III.1 assigns 7 frames (out of every 8 frames) for regular user traffic and 1 frame (out of every 8 frames) for priority user traffic.
A similar trend as that in Case II.1 can be observed in Figure 6. Although the probability of success for priority initial ranging degrades with higher initial ranging load, its performance is better than that of regular user.
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IEEE C802.16m-08/1046
Initial Raning Performance Analysis for 802.16e/m Networks
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0 0.5
1 1.5
2 2.5
3 3.5
4 4.5
5
Total IR Arrival Rate (= l t where t = 5 ms) priority IR success rate (III.1) reg interference (II.5) regular IR success rate (III.1) cc reg to reg (III.1)
5.5
6 pri interference (III.1) cc pri to pri (III.1)
6.5
7 7.5
8
Figure 6: Initial Ranging Performance Analysis for Cases III.1
2.2.2.3 Observation
In most of the cases, the excessive interference is the dominating factor of interference. As a result, division of the code space does not provide any benefit. Division of code space must be accompanied by dedicated time/frequency resources.
2.2.3 Guidelines a. Assign one or more dedicated initial ranging slot for regular user and one dedicated initial ranging slot for priority user for a larger channel bandwidth (e.g. 10 MHz). Also assign a set of dedicated codes for regular user and another dedicated set for priority user. b. Assign one or more dedicated initial ranging frames for regular user and one dedicated initial ranging frame for priority user for a smaller channel bandwidth (e.g. 5 MHz). c. The above guidelines are also applicable to bandwidth request.
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IEEE C802.16m-08/1046
2.2.4 Conclusion
The techniques used in Cases II and III are recommended. Case II requires the use of an additional initial ranging slot while Case III incurs additional delay (on the order of ten’s of ms) for initial ranging request.
ETS is a super set of all emergency services for an authorized select group of users. Wireless Priority Service (WPS) is one of ETS that is on wireless networks. The Wireless Priority Service should provide end-to-end treatment across the network ( e.g
., access, transport, and egress) so that higher communication session completion rates, as compared with public communication session completion rates, would be successfully achieved. Communication sessions in this context include voice, multimedia, and data.” [1]
DHS/NCS has worked with service providers as well as equipment vendors to get WPS implemented [8]:
 “Priority access service is intended to facilitate emergency response and recovery operations in response to natural and manmade disasters and events, such as floods, earthquakes, hurricanes, and terrorist attacks. Priority access service is also intended to support both national and international emergency communications.”
 “Priority access service is based upon, and complies with, the FCC Second Report and Order (R&O) 00-242 ( Wireless
Telecommunications (WT) Docket No. 96-86 ).
 “Priority access service is intended to allow qualified and authorized National Security and Emergency Preparedness (NS/EP) users to obtain priority access to radio traffic channels and core network resources during situations when Commercial
Mobile Radio Service (CMRS) provider network congestion is blocking call attempts”.
WiMAX network should provide the Priority Service too. The end-to-end priority service needs to cover radio accessing, data transportation and interconnection with other networks. Priority access service only focuses on the radio accessing part of the priority service. The NS/EP authorized user shall have higher priority level to obtain radio resource to access WiMAX network to facilitate emergency recovery.
End-to-end ETS is across different telecommunication networks and different countries. There are ETS standardization activities around the globe. The following standards bodies have ETS activities:
• ITU (International Telecommunication Union)
• IETF (Internet Engineering Task Force)
• ETSI (European Telecommunications Standards Institute)
• ATIS (Alliance for Telecommunications Industry Solution)
• TIA (Telecommunications Industry Association)
• 3GPP (3rd Generation Partnership Project)
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IEEE C802.16m-08/1046
• 3GPP2 (3rd Generation Partnership Project 2)
We address two types of calling scenarios. Scenarios are presented to develop the requirements and technical solutions for priority access.

Scenario 1: Mobile originating call. It is for authorized user to initiate a voice, data or video call to any party using
802.16m technology.

Scenario 2: Mobile terminating call. It is for authorized user to call another authorized user reachable using 802.16m technology.
The associated requirements for priority access service [1] include:
• Ubiquitous Services:
– Able to make a call/session in times of disaster, national emergency, or for executive/governmental communications relating to National Security / Emergency Preparedness (NS/EP).
– It applies to voice, video, and data services
• Availability:
• QoS
– It is available to NS/EP users at all times.
– End-to-end QoS should be provided based on 802.16e QoS classes and parameters
• Security
– “Networks must have protection against corruption and intrusion such as unauthorized access, control and traffic”
• Priority treatment
– “ETS communications should be provided preferential end-to-end treatment so that higher communication session completion rates, as compared with public communication session completion rates, would be successfully achieved”
Section 10 Medium Access Control Sub-Layer
10.x Network Entry
Assign one or more dedicated initial ranging slot for regular user and one dedicated initial ranging slot for priority user for a larger channel bandwidth (e.g. 10 MHz). Also assign a set of dedicated codes for regular user initial ranging and another dedicated set for priority user initial ranging.
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IEEE C802.16m-08/1046
Optionally, assign one or more dedicated initial ranging frames for regular user and one dedicated initial ranging frame for priority user for a smaller channel bandwidth (e.g. 5 MHz).
[1] “Overview of Standards in Support of Emergency Telecommunication Service (ETS),” ATIS-pp-0100009, November 2006.
[2]”Recommendations and Requirements for Networks based on WiMAX Forum Certified Products,” WiMAX Forum Release 1.5,
Jan. 2007
[3] D. Staehle and R. Pries, “Comparative study of the IEEE 802.16 random access mechanisms,” IEEE NGMAST, 2007
[4] D. J. Shyy, "Interference and Delay Analysis of Mobile WiMAX Networks", OPNETWORK Conference , Aug. 2008.
[5] J. You etal, “Capacity evaluation of the OFDMA-CDMA ranging subsystem in IEEE 802.16-2004”, IEEE 2005.
[6] S. Azizi and X. Yang, “Requirements for ranging sequences design for IEEE 802.16m,” C802.16m-UL_ctrl-08/013r1, 2008.
[7] “Wireless Priority Service (WPS) Industry Requirements Document for the Initial Operating Capability (IOC) for CDMA-based
System”, Feb. 2002.
[8] Wireless Priority Service (WPS) Industry Requirements for UMTS – Phase 1 – Redirection to GSM,” DHS/NCS IR Document,
Version 0.3, April 2005
[9] Quality of Service Attributes for Diameter,” draft-ietf-dime-qos-attributes-02.txt
[10] “Quality of Service Parameters for Usage with the AAA Framework,” draft-ietf-dime-qos-parameters-01.txt
[11] “RSVP Extensions for Emergency Services,” draft-ietf-tsvwg-emergency-rsvp-03.txt
[12] “QoS NSLP QSPEC Template,” draft-ietf-nsis-qspec-18.txt
[13] Report ITU-R.[PPDR]: “Radiocommunication objectives and requirements for public protection and disaster relief (PPDR)”
[14] Recommendation H.460.4 – Call priority designation for H.323 calls
[15] Draft recommendation H.SETS – security for ETS (H.235)
[16] E.106 – Description of an international emergency preference scheme (IEPS)
[17] Draft Recommendation U.roec – network requirements and capabilities to support ETS
[18] RFC3523: “Internet Emergency Preparedness (IEPREP) Telephony Topology Terminology”
[19] TETRA: “Mobile narrowband and wideband communications for public safety applications”
[20] TR41.4 TSB146: “Telecommunications – IP Telephony Infrastructure – IP Telephony Support for Emergency Calling Service)
[21] 3GPP TS 22.153, “Technical Specification Group Services and System Aspects; Multimedia priority service”, Release 8.
[22] 3GPP S.R0017-0, “Multimedia Priority Service (MMPS) for MMD-based Networks – Stage 1 Requirements”
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