Various flexible mechanisms related to quality of service （QoS） provisioning have been specified for uplink traffic at the medium access control （MAC） layer in the IEEE 802.16 standards. Among the mechanisms, cont...Various flexible mechanisms related to quality of service （QoS） provisioning have been specified for uplink traffic at the medium access control （MAC） layer in the IEEE 802.16 standards. Among the mechanisms, contention based bandwidth request scheme can be used to indicate bandwidth demands to the base station for the non-real-time polling and best-effort services. These two services are used for most applications with unknown traffic characteristics. Due to the diverse QoS requirements of those applications, service differentiation （SD） is anticipated over the contention based bandwidth request scheme. In this paper we investigate the SD with the bandwidth request scheme by means of assigning different channel access parameters and bandwidth allocation priorities at different packets arrival probability. The effectiveness of the differentiation schemes is evaluated by simulations. It is observed that the initial backoff window can be efficient in SD, and if combined with the bandwidth allocation priority, the SD performances will be better.展开更多
A dual S shaped micro strip antenna with a realistic feed is proposed for generation of tilted beam radiation pattern pertaining for beam steering applications. To achieve this, four feeding points are located at a di...A dual S shaped micro strip antenna with a realistic feed is proposed for generation of tilted beam radiation pattern pertaining for beam steering applications. To achieve this, four feeding points are located at a distance of 5.6 mm from the antenna centre. These feeding points when excited one by one generate four tilted beams in four different space quadrants, thus yielding a beam steerable antenna, Importantly, since the proposed antenna is symmetrical in the structure, all the four tilted beams have the same radiation pattern characteristics. A further enhancement of the antenna bandwidth is also achieved using 100-μn capacitive coupling between the feed and the antenna strip.展开更多
An analysis of WLAN security mechanisms of wired equivalent privacy （WEP） and Wi-Fi protected access （WPA） discovers that the current literature is not totally creditable in its judgment on the security value of W...An analysis of WLAN security mechanisms of wired equivalent privacy （WEP） and Wi-Fi protected access （WPA） discovers that the current literature is not totally creditable in its judgment on the security value of WEP and WPA. Based on the respective performances of WEP and WPA under certain typical attacks, this paper substantiates the judgment that WEP has quite a few vulnerabilities concerning confidentiality and integrity, but at the same time challenges the judgment on WPA with that WPA is robust enough to confront potential typical attacks and is not so unreliable as the current literature believes, although it has some vulnerabilities in its message integrity code （MIC）.展开更多
基金the National Basic Research Program(973) of China (No. 2005C13321804)
文摘Various flexible mechanisms related to quality of service （QoS） provisioning have been specified for uplink traffic at the medium access control （MAC） layer in the IEEE 802.16 standards. Among the mechanisms, contention based bandwidth request scheme can be used to indicate bandwidth demands to the base station for the non-real-time polling and best-effort services. These two services are used for most applications with unknown traffic characteristics. Due to the diverse QoS requirements of those applications, service differentiation （SD） is anticipated over the contention based bandwidth request scheme. In this paper we investigate the SD with the bandwidth request scheme by means of assigning different channel access parameters and bandwidth allocation priorities at different packets arrival probability. The effectiveness of the differentiation schemes is evaluated by simulations. It is observed that the initial backoff window can be efficient in SD, and if combined with the bandwidth allocation priority, the SD performances will be better.
基金the European Union through the Welsh As-sembly Government
文摘A dual S shaped micro strip antenna with a realistic feed is proposed for generation of tilted beam radiation pattern pertaining for beam steering applications. To achieve this, four feeding points are located at a distance of 5.6 mm from the antenna centre. These feeding points when excited one by one generate four tilted beams in four different space quadrants, thus yielding a beam steerable antenna, Importantly, since the proposed antenna is symmetrical in the structure, all the four tilted beams have the same radiation pattern characteristics. A further enhancement of the antenna bandwidth is also achieved using 100-μn capacitive coupling between the feed and the antenna strip.
文摘An analysis of WLAN security mechanisms of wired equivalent privacy （WEP） and Wi-Fi protected access （WPA） discovers that the current literature is not totally creditable in its judgment on the security value of WEP and WPA. Based on the respective performances of WEP and WPA under certain typical attacks, this paper substantiates the judgment that WEP has quite a few vulnerabilities concerning confidentiality and integrity, but at the same time challenges the judgment on WPA with that WPA is robust enough to confront potential typical attacks and is not so unreliable as the current literature believes, although it has some vulnerabilities in its message integrity code （MIC）.
