Design comparison between HiperLAN/2 and IEEE802.11a services

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This paper is a study and comparison between the two Wireless LAN (WLAN) standards HiperLAN/2 and IEEE 802.11a. WLANs are used instead or together with ordinary LANs to increase mobility in for example an office. HiperLAN/2 is an European standard developed by ETSI and the IEEEs standard is American. A WLAN-card consists roughly of a Medium Access Control (MAC), Physichal layer (PHY) and an antenna. The antenna is the same for the different standards. Both standards operates at 5.4 GHz with a maximum transmission rate at 54 Mbit/s and they use OFDM to modulate the signal. This means that the physical layer in the two standards is similar. The differences between the standards are in the Medium Access Control (MAC) layer. HiperLAN/2 has a much more complex MAC since it is developed with the starting point in cellular phones. Therefore this MAC is not very similar to ETHERNET that is the protocol used by regular network. On the other hand it is built to be compatible with cellular phones and other applications. The 802.11a MAC is very much the same as in the 802.11b standard that is the most used standard at present. The difference is that 802.11a can send at much higher data rates. This MAC is build with starting point in ETHERNET so it has a similar interface to the computer. This makes it less complex. The different MACs can provide different services. The greatest difference is that 802.11a can use a distributed send mode where any STA can send if the medium is idle. This reminds a lot of ETHERNET but they use different methods to sense if the medium is idle. In HiperLAN/2 are all transmissions scheduled by the AP. 802.11a can operate in a similar way but at the moment this mode is not as fully developed as in HiperLAN/2. There are working groups in IEEE that works toward an improvement of 802.11a so it can use queues with different priorities, this is already implemented in HiperLAN/2. Another important issue in wireless environment is security. Both standards use encryption to protect their messages. The difference is that HiperLAN/2 changes their encryption key for every connection where 802.11a uses the same key the whole time. This gives HiperLAN/2 a better security with todays standard but thereare working groups dealing with implementing key-exchange functions and Kerberos use in 802.11a. Chapter 8 ...