Beamforming

Beamforming is the smart antenna technology  . Beamforming transmits power only in desired direction i.e the power is directed in the direction of user.

In point to multipoint scenario it saves the unnecessary transmission of power.

Interference due to multiple path i.e ISI can be avoided by using beamforming , As antenna transmitsin the direction of user so there is no other path of radio transmission to that user , so no multiple path and so no multiple path interference.

OFDM is also a way to avoid multiple path interference . OFDM infact takes the advantage of multiplepath interference.


Please go through OFDM multiple path mitigation capability to understand about its working.

Fixed and Mobile Wi-max

Fixed Wimax ( Worldwide Interoperability for microwave access) is IEEE 802.16d standard , Fixed wimax means that CPE has to be fixed at one place and latched to the base station from which it has to communicate . In fixed Wimax base station and CPE , both are installed outside that is both are outdooe device . one CPE is associated with one base station only and one base station can be associated with more than one CPE's.

Mobile Wimax is 802.16e standard . In mobile Wimax , Base station base station is fixed but cape can be movable , here CPE can be the outdoor device or it can be dongle.

As CPE moves from coverage range of one base station to another base station , The CPE can be latched with another base station without any communication break , this process is known as handoff , here CPE compares the signal strength between the two base station and associates itself with the base station having strongest signal strength when the weaker signal strength falls below the threshold level , The process of handoff is controlled by ASN ( Access service network) i.e ASN is responsible for handoff without any communication  break.

OFDM V/s OFDMA

OFDM stands for Orthogonal Frequency Division Multiplexing . OFDM is one of the feature of Wimax 802.16d standard developed for fixed wimax.

OFDM is used in point to point connectvity . For two way data transmission OFDM is used with TDD (Time Dicision Duplexing)

OFDMA stands for Orthogonal Frequency Division Multiple Access. OFDMA is point to multipoint version of OFDM . OFDM is multiplexing and OFDMA is multiple access where multiple CPE's can be connected with same base station.

In OFDMA fixed wimax point to multipoint connectivity , uplink transmission ( CPE to base station ) can be OFDM because one CPE can be conneced to one base station only , but in downlink transmission ( Base station to CPE) is OFDMA as one base station is connected to many CPE's.

Wi-Fi and Wi-Max

Wi-Fi stands for wireless fiedility and Wi-Max stands for World Wide Interoperability for Microwave Access.

Wi-Fi and Wi-Max are the technologies to access internet over the wireless.

Wi-Fi is wireless LAN technology that operate over the unlicensed frequency band . Wi-Fi provides connectivity within the campus i.e in LAN local area network.

Standards developed for Wi-Fi are 802.11a , 802.11b , 802.11g , 802.11n , 802.11ac.


Wi-Max in wireless WAN technology that can operate over licensed and licensed frequency band . the throughput per user can be much higher than Wi-Fi .

Wi-Max can be used to connect two or more Wi-Fi hotspots . It can be used to provide backhaul to the Wi-Fi access point.

802.16 d and 802.16 e are the standards developed for Wimax. 802.16d is for fixed Wi-Max and 802.16e is for mobile Wi-Max.

Bandwidth , Modulation and Data Rate.

Bandwidth is the range of frequency or band of frequency i.e the difference between the highest and the lowest frequency over which the data is to be transmitted.

Data rate is the rate at which data is transmitted from one point to another.


Modulation is the alteration in the characteristic of carrier frequency as per the baseband frequency , In digital communicationthe data rate depends on the selected modulation level.

The data rate will be lowest at BPSK and it will increase as we move towards the higher modulation level QAM64 , QAM 128 ...but the coverage range at same transmit power will decrease.

Larger channel bandwidth , higher modulation level and greater transmit power yields higher data rate.

BPSK   --- 1 bit / symbol
QPSK ---- 2 bit/ symbol
QAM 16  -- 4bit/symbol
QAM64 ---  6 bit/symbol.
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Point to Multipoint Wireless Communication

Point to multipoint as the name suggests , a single point can be connected to many other points.

IN WAN point to multipont connectivity , the centre point is known as the base station and in LAN connectivity it is known as the access point.

Here I will discuss about the WAN connectivity . At microwave frequencies , 60% of the first Fresnel zone must be clear for good signal strength.

The base station is the center point so it has to be configured (frequency , channel bandwidth , IP etc) first of all and installed at the height and azimuth as per the survey report.

Other devices known as CPEs are to be configured afterwards and should be with in the coverage range as per the survey report .

In point to multipoint connectivity the base station use to have the sector antenna of azimuth 30deg , 60 deg , 90 deg , 120 deg and Omnidirectional antenna , so the CPE must be within the coverage ange of the base station for which it is configured.

The range ( link distance ) depends on the antenna parameters.

Point to Point Wireless Communication.

Point to point communication means one point can be connected to only one another point.  At microwave frequencies at least 60% of the first Fresnel zone must be clear for good signal strength .

The device has to selected according to the link distance and data rate that is required.

As per the device specification if it is FDD we require two different frequencies for one point to point link , we have to configure the device  ( Radio ) with one uplink and one downlink frequency ,  It has to be configured on both the devices ( Radios ) so that communication can take place over those frequencies.

Another configuration is SSID ( System identifier) , SSID must be same on both the radios , IP must be configured so that reachability can be checked and also so that we can access the radio and tehre are some other configuration that varied from radio to radio.

If the device is TDD then same frequency must be configured on both the devices and both the radios must have same SSID, same channel channel bandwidth , rest of the confiduration depends on radio to radio .
Again the radio must be provided with IP so that it can accessed and reachability can be checked .

The range ( Distance of point to point link ) and data rate depends on antenna parameters.