7.2 The choice of the equipment of base stations

Consider options for the development of WiMAX base stations on the basis of known chips. Fujitsu has developed a chip MB87M3400 for both base and subscriber stations. However, unlike Intel, Fujitsu chip has an interface to the external processor. To implement full-duplex mode you want to use two chips, one of which functions as a physical layer and lower MAC layer Protocol, and the second is an external processor (third party company) for implementation of the top level of the MAC Protocol. To develop base stations Fujitsu provides a debug kit that implements a full-duplex mode of operation, processor Freescale MPC8560, but does not supply software that provides the functions of the upper MAC layer Protocol.

The company PicoChip offers a solution PC102/PC8520, built on two of its parallel processors PC102. The company provides software that implements the physical layer and lower MAC layer Protocol chips on the PC102. And Fujitsu, the company uses PicoChip Freescale MPC8565 to implement top-level MAC Protocol in your debug kit. However, unlike the Fujitsu, PicoChip has licensed its software to the top of the MAC layer Protocol. Since the decision PC102/PC8520 not embedded encryption-decryption, for their implementation should be used by the external processor.

Chip for the development of base stations SQN2010 company Sequans is the first "system on a chip" having a full-duplex mode. SQN2010 implements all the functions of the physical and MAC levels required for full-duplex operation of the base station. Chip SQN2010 different from SQN1010 presence of a second CPU that implements the top level of the MAC Protocol. On the chip SQN1010 provides a PCI interface to allow the connection of external processor.

The decision DM256/MC336 of Wavesat company can be used to develop base stations. This solution supports full duplex mode, but it should be noted that the implementation of encryption-decryption it requires an external processor. Like Fujitsu, Wavesat provides no software support for the upper MAC layer Protocol required to develop base stations.

Of the four solutions described only chips PicoChip PC102 not integrate in themselves the functions of the ADC/DAC. Therefore, for developments that use analog radio interface, you also require a device ADC/DAC. The main parameters of the considered solutions for the development of base stations is presented in table. 3 [6].

Table 7. The main parameters of the considered solutions for the development of WiMAX base stations.

Option	Fujitsu MB87	PicoChip PC102/PC8520	Sequans SQN2010	Wavesat DM256/MC336
Function	PHY/MAC	PHY/MAC	PHY/MAC	PHY/MAC
Maximum channel width	20 MHz	10 MHz	28 MHz	10 MHz
The number of chips	1 chip 1 chip	2 chip 2 chip	1 chip 1 chip	1 chip 1 chip
TDD	Mill, 32-bit generic	Mll	RMLL, PCI	PCI
FDD	Analog and digital	digital	Analog and digital	Analog and digital

The choice of the manufacturer of chips for the development of WiMAX systems is an important strategic decision. For fast and effective system development requires the most complete hardware and software support and tools for development and debugging. The presence of the debug kits can significantly increase the speed and reduce the cost of development of WiMAX equipment, which is one of the main criteria when choosing a product.

Deploying WiMAX systems:

Building a network of fixed wireless access involves the use of three types of equipment - base stations, subscriber stations and equipment for communication between base stations.

To two or more radio signals do not interfere with each other's work, it is necessary that they coincide (overlap) in the frequency (frequency spectrum), time and space. Thus, each system for its proper functioning must be frequency-territorial spacing (CHTR) with interfering signal (interference). In addition, since we are dealing with digital systems, the radio signals which have a pulse shape, the condition of the timing means the coincidence or overlap in time of the pulses of the signals coming into the system. Thus, the time spacing of the pulses of the signals can be provided time synchronization of system operation with sources of interference.

Network standard IEEE 802.16 WiMAX are by far the most high-tech system BWA in the field of wireless telecommunications and place high demands on the parameters and quality of your antenna-feeder tract. Antenna and microwave circuitry in General is the most capricious part of any wireless access systems, in the case of WiMAX, the incorrect integration of active equipment and microwave can nullify all advantages of this technology. In base stations of WiMAX networks can be used Omni-directional and sector antenna with a sector angle of 60, 90 and 120 degrees.

When installing base stations uses the existing infrastructure.

Figure 24 - Typical operating circuit WiMAX BS placed on the existing sites using BWA NGN transport channels

The location of the WiMAX sites should be selected in such a way as to ensure maximum performance. From the standpoint of operating efficiency, special attention should be paid to operational support, deployment platforms, as well as their standardization. This saves time and money spent on the design of each individual site. Standardization involves the creation of a small set of configurations, which are taken as finished projects and adjusted with minimal changes to the specifics of a particular site. On the market there are inventory solutions that support the automation of this process. Special attention in such decisions should be given to the updating of inventory data, because in the future they will be required to expand the WiMAX sites as demand growth and to guarantee a high level of service.