求高手翻译一段英文,200分!不要软件翻译的,能看出来的,如果好的话还会追加分数! Cognitive radios that are employed in a network with dynamic frequency assignments must operate efficiently in the presence of uncertainti

求高手翻译一段英文,200分!不要软件翻译的,能看出来的,如果好的话还会追加分数! Cognitive radios that are employed in a network with dynamic frequency assignments must operate efficiently in the presence of uncertainti
求高手翻译一段英文,200分!
不要软件翻译的,能看出来的,如果好的话还会追加分数!
Cognitive radios that are employed in a network with dynamic frequency assignments must operate efficiently in the presence of uncertainties and variations in the propagation
characteristics of the network’s communication links. A lowcomplexity adaptive transmission protocol is described and evaluated for use in cognitive radio networks whose links have
unknown and possibly time-varying propagation losses as a result of such phenomena as slow fading or variations in shadowing. The cognitive radios are required to derive only simple statistics in the receivers in order to provide the information that is needed by our protocol; no estimates or measurements of received power or channel gain are used. The protocol’s primary mechanism for responding to changes in propagation loss is to adjust the modulation and coding. Because of disruptions that can be caused by higher levels of interference to other radios in the network, the transmitter power is increased only if the most powerful combination of coding and modulation is inadequate. We employ finite-state Markov models for slowly varying channels, and we demonstrate that for such channels our protocol performs nearly as well as an ideal protocol that is told the exact value of the propagation loss for each packet transmission. Thus, the additional complexity that is required to enable cognitive radios to obtain precise channel-gain estimates is not justified and would lead to only negligible improvement in throughput. The throughput of our adaptive transmission protocol is compared with an upper bound that is derived from information theory for a hypothetical ideal protocol that is given perfect channelstate information, and some preliminary results on learning the adaptation decision intervals are included.

求高手翻译一段英文,200分!不要软件翻译的,能看出来的,如果好的话还会追加分数! Cognitive radios that are employed in a network with dynamic frequency assignments must operate efficiently in the presence of uncertainti
此答复请楼主绝对放心,我看你也是十级高手,定能明鉴.
COGNITIVE radios are ideally suited for use in dynamic spectrum access networks in which there may be large variations in channel conditions from one session to the next.Such variations are common in networks that operate in a fixed frequency band,but the variations are more severe if the frequency band is changed for consecutive sessions.Each radio in a dynamic spectrum access network must be aware of its communication environment,and it must provide the information that other radios need in order to communicate with it efficiently.This information should besimple,easy to derive,and easy to send to neighboring radios.We focus on the information needed to adapt the error-control coding,modulation,and transmitter power for half-duplex packet transmissions.
认知无线电能理想地适用于动态谱接入（访问）网,在这种网络中,信道条件从一个会话（作业阶段）到下一个会话可能存在很大变化.这样的变化在以固定频带工作的网络中是常见的,但是如果频带对连续的会话来说是变化的,那么这样的变化就会更严重.在一个动态谱接入网中的每一无线电必须感知到自己的通信环境,而且它必须提供其它无线电所需的信息,以便与其有效地通信.此信息应该是简单的,容易导出的,以及容易发送到临近无线电的.我们重点讨论为适应错误控制编码、调制、以及半双工包传输用发射机功率所需的信息.
A new session begins when one radio,referred to as the source,has a collection of packets to send to another radio,the destination.At the start of a new session,which may be in a different frequency band than the previous session,the protocol must adjust the transmitter power to provide reliable communications with minimal energy consumption and minimal interference to other radios.As the session progresses,the protocol must adjust the transmissions to compensate for changes in channel conditions.Our results demonstrate the extent to which the adaptive transmission protocol can rely only on code-rate adaptation to offset increased propagation loss.We show that when the cognitive radios must compensate for very large variations in the channel conditions,it is necessary to adapt the modulation also.Power increases are employed by our protocol only if the channel deteriorates so much during a session that changes in coding and modulation cannot provide enough compensation,which occurs very rarely.
一个新的会话开始于一个作为源的无线电拥有一批包要发送到另一无线电（目的地）时开始.在可能处于与前一会话不同频带的新的会话开始之际,协议必须调节发射机的功率,以便为可靠的通信提供最小的能耗及对其它无线电最小的干扰.随着会话的进展,协议必须调节传输来补偿信道条件的变化.我们的结果证明了自适应传输协议能够仅依赖编码率自适应来弥补增加了的传播损耗的程度.我们证明了,当认知无线电必须补偿信道条件很大的变化时,也就必须自适调制.只要信道在一次会话过程中恶化到编码和调制的变化不能提供足够的补偿,我们的协议就采用功率的提高,不过这种情况很少发生.
The throughput performance of our protocol is compared with theoretical limits that are derived from considering ideal protocols and applying Shannon capacity results.We demonstrate that our protocol performs nearly as well as an ideal protocol that is given perfect channel-state information.The modulation formats that are available to the adaptive transmission system span a range from bandwidth-efficient modulation to power-efficient modulation,which permits the adaptation to compensate for large changes in propagation loss.In order to keep the complexity low,bit-interleaved coded modulation is employed to obtain each combination of coding and modulation that is used by the adaptive transmission protocol.In this approach,it is simple to change the code and modulation independently,because the error-control codes are not tailored to specific modulation formats.
我们的协议的吞吐量性能与理论极限做了比较,理论极限则通过考虑理想的协议和采用Shannon（香农）容量结果推得.我们证明了,我们的协议的性能和被提供理想信道状态信息的理想协议几乎一样好.可用于自适应传输系统的调制格式的范围从带宽－有效调制跨越到功率有效调制,这就使自适应能补偿传播损耗大的变化.为了使复杂性保持在低水平,采用位－间插复用的（interleaved）编码调制来获得为自适应传输协议所采用的编码和调制的每一组合.用这一方法,独立地改变编码和调制就很简单,因为错误控制代码不是为特定的调制格式定制的.