IEEE 802.11 is the first standard for WLAN products from internationally recognized independent org

IEEE 802.11 is the first standard for WLAN products from internationally recognized independent organization. IEEE manages most of the standards from the wired LAN. This represents an important milestone in the development of WLAN networks, as users can have a unified and standardized products. This allows a significant reduction in the price of the final product and hence widespread WLAN products. Set of WLAN products marketed in the frequency range 900MHz and 2,4 GHz, as there are solutions in the range of 5,4 GHz. The latter frequency is controlled by 802.11 and HIPERLAN / 2. WLAN products include wireless adapters connected to a standard LAN network called. access points (access point) via PCMCIA, ISA, USB or other PC based platforms. Most products, however, are created on the basis of their own decisions, forcing buyers 3m 467mp to use the services of a single company. A standard allows for the type of structure used, which creates conditions for increased competition and hence reduce the cost of WLAN products. Areas of possible spread of WLAN networks is shown in Fig.1.4. 3m 467mp
IEEE 802.11 standard defines protocols for two types of networks: Ad / hoc and client \ server networks. Networks such as Ad / hoc networks are relatively 3m 467mp simple, where communications take place between 3m 467mp multiple stations in a given area of coverage without the use of access points and servers. Standard precisely defines the label to adhere to each station as they have free access to the transmission medium.
The standard also provides methods for arbitration of access 3m 467mp to the middle so that the transmission 3m 467mp speed to maximum for all users in a given area. Networks such client 3m 467mp / server (fig.1.5) using access 3m 467mp points that control the distribution of the data to all stations and allows mobile stations to move from one cell to another. The access point is used for controlling traffic from the mobile station to a wired subscriber, or other user of the wireless client / server networks. This type of traffic control allows precise 3m 467mp coordination 3m 467mp of the mobile station in a service area of a base station and properly communicating information. 3m 467mp Access point distributes data between stations 3m 467mp and other wireless subscribers or other network 3m 467mp servers. Usually WLAN networks 3m 467mp are controlled by a central access 3m 467mp point, which provides a higher speed of information transfer.
The physical layer in each network 3m 467mp defines modulation and signal transmission characteristics danni.Vav the physical layer of WLAN networks using two RF (radio frequency) method and an IR (infrared). Operation of WLAN devices in an unauthorized band requires the use of directly modulated spread spectrum (DSSS), to meet the standards in most countries. RF data is of two types - a jump frequency (Frequency Hopping - FH) and Direct Spread Spectrum (Direct Sequence spread spectrum - DSSS). Both architectures are determined to work in 2,4 GHz (ISM) frequency band. Both occupy a bandwidth of 83MHz, as the band stretches the limits 2,4000 - 2,4835 GHz. In the method, direct spread spectrum, the differential BPSK (DBPSK), and the differential QPSK (DQPSK) modulation. Method with a jump of frequency using Gaussian FSK 2-4 levels. Types of modulation 3m 467mp used and the speed of data transmission is shown in Table 1. Used standard also limits the gain of the antenna to 6dBi maximum. The radiated 3m 467mp power is also limited by these boundaries are different for different countries. Maximum 3m 467mp radiated power is shown in the Table. 2.
4 and 8 (0,72 μs)
192 and 216 (4μs)
For infrared standard that operates in the range 850-950nm, using the peak radiated power of 2W. The type of modulation is pulse - positional modulation (pulse - positioning modulation - PPM) for 4 or 16 levels. From Table 2 it is seen that in different countries use different 3m 467mp frequency bands for the operation of a WLAN network. This circumstance is imposed due to the different distribution of frequency ranges and different standards for electromagnetic compatibility.
At the physical layer standard DSSS uses 11 bit Barker sequence to broaden before sending the data over the airwaves. This results in the output of the 11 symbols of each symbol supplied to the input of the transmitter, which allows to minimize the effect 3m 467mp of multipath and interference from other transmitters. The use of the Barker code of the expansion of the spectrum provides a coefficient of expansion 10,4 dB