3gpp tsg geran adhoc #2 gahw-000034 Munich, Germany Agenda Item 3 October 9-13, 2000
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| 3GPP TSG GERAN Adhoc #2 GAHW-000034
Munich, Germany Agenda Item 6.1.3 October 9-13, 2000
1IntroductionIn GERAN R4, streaming and conversational bearers over PDTCH are supported [1]. Two mechanisms for supporting these bearers were described in previous Lucent GERAN contributions [2,3]. For streaming, R’99 acknowledged mode procedures have been enhanced in order to realize a limited retransmission (LRTX) mode that implements selective ARQ based on data delivery delay constraints [3]. For conversational bearers, unacknowledged mode procedures are enhanced to realize a repeated MCS (RMCS) mode where multiple copies (each with different parity) of an RLC block [2] are transmitted for soft combining at the receiver. LRTX and RMCS reuse GSM R99 EGPRS functionality for the following:
For LRTX and RMCS, an additional functionality must be specified: maintaining a negotiated QoS. In this contribution, various QoS parameters for bearer establishment and maintenance are described. Signaling flow and feedback message requirements are also discussed. 2RB QoS ParametersEach streaming and conversational class bearer must deliver a grade of service that is acceptable to the user. The RB QoS parameters quantify an acceptable grade of service. For conversational and streaming class RBs, the relevant QoS parameters are play out rate, residual loss rate, maximum delivery delay, and maximum fill delay. RB QoS parameter definitions are provided in Table 1. Some parameters are negotiated at bearer setup while others are dynamic during the life of the RB.
Table 1: QoS Parameter Definitions After RB setup, the negotiated QoS parameters are satisfied by the RLC. Upon receipt of an RLC block, a receiver stores the soft information for blocks received in error—even when operating in unacknowledged RLC mode—for a time no less than the maximum delivery delay. The maximum fill delay parameter minimizes the channel occupancy without violating the negotiated QoS parameters1. The maximum fill delay is a function of the negotiated QoS parameters, the MCS payload size, and the channel quality. The maximum fill delay is given by  , where for LRTX,  = the minimum time necessary for the successful retransmission (of 100%-L) of RLC blocks received in error and, for RMCS, = the minimum time span of the sub-block interleaving scheme necessary to achieve the negotiated residual loss rate. Since the network is the only entity that has channel quality estimates for both the uplink and the downlink, either the network must signal the UL maximum fill delay to the MS, or the UL maximum fill delay must be pre-defined to a value that does not violate the negotiated QoS parameters.
3Downlink Flow Procedures3.1DL SetupUpon DL RB setup, the following QoS parameters are negotiated: play out rate, residual loss rate, and maximum delivery delay. The values of these parameters are fixed for the duration of the RB. 3.2DL Management3.2.1LRTXThe network dynamically determines the best choice of MCS and maximum fill delay. The DL MCS MAC header identifies the prevailing MCS, puncturing scheme, and BSN for each transmitted block. The network ensures that all RLC block retransmissions occur within the maximum delivery delay. 3.2.2RMCSThe network dynamically determines the best choice of MCS, maximum fill delay, the number of RLC block repetitions (each repetition using a different puncturing scheme), and the RLC sub-block interleaving scheme. The network does not require any new mechanisms to signal the dynamic parameters. As per GSM R99, the DL MCS MAC header identifies the prevailing MCS, puncturing scheme, and BSN for each transmitted block. The network ensures that all RLC block repetitions occur within the maximum delivery delay. 3.3DL Feedback3.3.1LRTXLRTX uses most of the procedures of the RLC acknowledged mode. The MS sends DL Ack/Nack messages as directed by the network. Also at the direction of the network, the MS provides DL channel measurement reports (MEAN_BEP & CV_BEP). For both the DL Ack/Nack and the DL channel measurement reports, the MS uses GSM R99 reporting mechanisms. 3.3.2RMCSRMCS uses most of the procedures of the RLC acknowledged mode. At the direction of the network, the MS provides DL channel measurement reports (MEAN_BEP & CV_BEP). For the DL channel measurement reports, the MS uses GSM R99 reporting mechanisms. 4Uplink Flow Procedures4.1UL SetupUpon UL RB setup, the following QoS parameters are negotiated: play out rate, residual loss rate, and maximum delivery delay. The values of these parameters are fixed for the duration of the RB. 4.2UL Management4.2.1LRTXThe network dynamically determines the best choice of MCS and the maximum fill delay. The network updates these parameters simultaneously; the parameters are signaled only if changes are necessary. The existing channel coding command mechanism by which the network signals the choice of UL MCS is sufficient. The maximum fill delay can either be set to a default value or signaled by adding an optional 2 bit field to the Packet Uplink Ack/Nack and Packet Timeslot Reconfigure messages. Two bits should be sufficient to cover the dynamic range of interest of the maximum fill delay parameter. The UL MCS MAC header identifies the MCS, puncturing scheme, and BSN for each transmitted block. The MS ensures that all RLC block retransmissions occur within the maximum delivery delay. 4.2.2RMCSThe network dynamically determines the best choice of MCS, the number of RLC block repetitions, and the maximum fill delay. The network updates these parameters simultaneously; the parameters are signaled only if changes are necessary. The existing MCS mechanism by which the network signals the choice of UL MCS is sufficient. The maximum fill delay and number of RLC block repetitions can be indicated through optional 2 bit fields in the Packet Uplink Ack/Nack and Packet Timeslot Reconfigure messages. The maximum fill delay can also be set to a default value. The UL MCS MAC header identifies the MCS, puncturing scheme, and BSN for each transmitted block. Given the prevailing MCS, the number of RLC block repetitions, and the negotiated maximum delivery delay, the MS chooses an RLC sub-block interleaving scheme that maximizes time diversity. The MS ensures that all RLC block repetitions occur within the maximum delivery delay. 4.3UL Feedback4.3.1LRTXLRTX uses most of the procedures of the acknowledged RLC mode. The network sends UL Ack/Nack messages to the MS via the existing mechanism in GSM R99. 4.3.2RMCSRMCS uses most of the procedures of the unacknowledged RLC mode. No RMCS UL Ack/Nack feedback is necessary. 5Conclusions & RecommendationsA summary of the RB QoS parameters, the RLC procedures, and newly required mechanisms for LRTX and RMCS is given in Table 2. Lucent Technologies recommends that these parameters and procedures be adopted to realize both a limited retransmission RLC mode and a repeated MCS RLC mode for streaming and conversational bearers, respectively.
Table 2: Summary of LRTX & RMCS RLC procedure requirements. References [1] 3GPP TSG GERAN Tdoc 471/00, “GERAN Overall Stage 2 Description,” Rapporteur. [2] 3GPP TSG GERAN Adhoc Tdoc 084/00, “Repeated MCS4, MCS7 and MCS9 for Streaming and Conversational Bearers,” Lucent Technologies. [3] 3GPP TSG GERAN Tdoc 116/00 “RLC with Limited Retransmissions for Streaming Service Class,” Lucent Technologies. [4] ETSI GSM 04.60 R’99, “General Packet Radio Service (GPRS); Mobile Station - Base Station Interface; Radio Link Control/Medium Access Control (RLC/MAC) protocol.” 1 A fill delay of zero corresponds to “Send on Demand.” |