Question

外文翻译 翻译成中文，要语句通顺正常逻辑的

Abstract—Opportunistic Spectrum Access (OSA) allows
unlicensed users to share licensed spectrum in space and time
with no or little interference to primary users, which bring new
research challenges in MAC design. In this paper, we firstly
introduce the differences between the conventional multi-channel
MAC protocols and the MAC protocols for OSA as well as the
requirements for OSA MAC protocols, and then analyze and
compare the several MAC protocols proposed so far in the
literature. At last we give the characters of these protocols.
Keywords- Cognitive radio; opportunistic spectrum access;
dynamic spectrum access; multi-channel; MAC protocol
I. INTRODUCTION
Currently, the spectrum is allocated to licensed users with a
static manner, while the spectrum demand nowadays for GSM,
WLAN, WiMAX etc is increasing. The traditional allocation
policy faces spectrum scarcity in particular spectrum bands.
But under the observation of the Federal Communication
Commission (FCC) [1], it was shown that over 70% of the
allocated spectrum is not used at any given time even in a
crowded area where the spectral usage is intensive. The
concept of cognitive radio has been proposed to make use of
the unused spectrum at a given time and place. In cognitive
radio networks, unlicensed (secondary) users can make use of
licensed frequency bands without violating the licensed
(primary) users. In cognitive radio wireless networks,
secondary users do not have pre-assigned frequency bands but
they opportunistically search, find and operate in an available
band without constraining the primary users.In order to resolve
the scarce spectrum problem, better spectrum management
strategies should be adopted in cognitive radio wireless
networks. For unlicensed users are allowed to opportunistically
access the licensed spectrum band without or with little
interference to licensed users, the nature of cognitive radio
networks demands dynamic spectrum access.
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Answer 1

抽象的机会主义频谱接入（OSA）的允许无牌用户共享空间和时间，没有或很少干扰的主要用户，这在MAC设计带来新的研究许可频谱的挑战。在本论文中，我们首先介绍传统之间的多通道MAC协议和露天茶座的MAC协议，以及露天茶座的MAC协议的要求，然后进行分析和比较几种MAC协议在文献中提出至今的差异。最后我们给出了这些协议的字符。关键词，认知无线电;机会主义频谱接入，动态频谱接入，多通道; MAC协议，导言目前，频谱分配与静态的方式授权用户，而现在的GSM，无线局域网，WiMAX的频谱需求不断增加等。传统的分配政策，特别是面临着频段频谱稀缺。但是，根据联邦通信观察委员会（FCC）[1]，结果表明，超过70％的频谱分配的不针对任何特定时间使用，即使在拥挤的地方是密集的频谱的使用。认知无线电的概念已经提出要在特定时间和地点未使用的频谱的使用。在认知无线电网络，无牌（二级）的用户可以在不违反许可（小学）的用户使用许可频率波段。在认知无线电的无线网络，二级用户没有预分配的频率波段，但他们投机搜索，查找并在可用频段，不受制约的主要users.In为了解决频谱的稀缺问题，更好的频谱管理策略应采用在认知无线电的无线网络。无牌用户允许的情况下访问或投机，很少干扰授权用户的许可频段，认知无线电网络的性质要求的动态频谱接入