IEEE802.11e无线联网标准

   在CFP中改进的信道访问和维持轮询向后兼容性的能力,带来了更高效率的轮询。另外还包括了传输调度和单一命令中链接轮询序列的能力。
  
     这些机制提供了最大效率的高带宽数据流、电力管理友善实现以及对可变位速率和脉冲式数据流的轮询式访问。
  
     QoS基线中采用的集中式调度器保证了避免冲突,因此,改进了传送时间关键的负荷的能力。承诺重要的QoS合约(如延迟、抖动和带宽)的能力也大为改进。信道访问与由子网带宽管理器(类似于更高层的协议和机制)完成的分配联系在一起,因此获得了更高的系统可靠性。
  
   无线系统中信道的健壮性是一个重要的考虑因素,因为噪声、干扰和多路径效应在2.4GHz和5.xGHz频段上导致信道吞吐量的变坏,负面地影响了对滞后敏感的和高带宽的流量(如语音和视频)的可靠传输的能力。
  
     人们对改进信道的健壮性特别关注。提议的方案包括FEC(正向纠错)和选择性重发。这些机制包含了在每个数据流的基础上制定纠错、确认和重发政策的能力,从而通过针对每种类型数据流专门制定政策的方式,适应了多种不同的数据流类型。
  
     通过FEC、有选择重发的滞后确认和动态信道变化,信道的吞吐量得到大大改进。甚至在企业环境中部署了大量的无线子网时,基线的那些必进仍能支持QoS。在这样的环境中,多个IEEE802.11e子网可能共存于各个无线电覆盖的范围内,在不同子网中的设备进行通信时,会引起干扰和(或)冲突。
  
     QoS基线尚未获得批准。在这一过程中,下一步是批准规范草案,然后是批准最终的规范。
  
   Improved channel access during CFP, and the ability to retain polling for backward compatibility, result in more efficient polling. The ability to schedule transmissions and chain a sequence of polls in a single command is included.
  
   These mechanisms provide for maximum efficiency for high-bandwidth streams, power-management friendly implementations, and poled-style access for variable bit rate and bursty streams.
  
   The centralized scheduler used in the QoS Baseline guarantees collision avoidance and, therefore, improved ability to deliver time-critical payloads. The ability to honor critical QoS contracts such as latency, jitter and bandwidth is much improved. Channel access is tied to the allocations made by subnet bandwidth manager –like higher layer protocols and mechanisms so system reliability is achieved.
  
   Channel robustness in wireless systems is an important consideration because noise, interference and multipath effects lead to degraded channel throughput in the 2.4GHz and 5.xGHz bands, adversely affecting the ability to reliably transmit latency-sensitive or high-bandwidth traffic such as voice and video.
  
   Special attention was paid to improving channel robustness. The proposed schemes include FEC and selective retransmission. These mechanisms include the ability to specify the correction, the ability to specify the correction, acknowledgement and retransmission policy on per-stream basis, thereby accommodating a range of traffic types with policies designed specifically for each.
  
   Channel throughput is improved through FEC, delayed acknowledgements with selective retransmissions and dynamic channel change.
  
   The Baseline enhancements support QoS even when wireless subnets are deployed densely, as in enterprise environments. In such environments, multiple IEEE802.11e subnets could be located within radio range of each other, which would cause interference and/or collisions during the communications by devices in different subnets.
  
   The QoS Baseline has not been approved yet. The next steps in the process are the approval of a draft specification, followed by the approval of the final specification.