A Study On Antenna Hopping

Maximum ratio combining SIMO: This form of SIMO takes both signals and sums them to give the a combination. In this way, the signals from both antennas contribute to the overall signal.

In Fig. 1, the 4 nodes are considered. Among the four nodes 2 of the nodes (Node 1 and Node 2) are primary networks and 2 other nodes (Node A and Node B) are secondary networks. The two networks act in different frequency range. The primary network acts at a range of 2.4GHz - 2.4835GHz range. The secondary network acts at a range of 433MHz - 473MHz represents the block diagram of the proposed system. The use of different frequencies increases the number of users. Node 1 and Node 2 communicate at 2.4GHz and Node A and Node B communicate at 433.9MHz. The nodes are made mobile and this causes high interference. This is cancelled by channeling where the frequencies are slotted. Multi-hop cognitive radio technique occurs when the data is transmitted from one secondary node to another which is out of range via primary node. At that time the primary node which is of MIMO antenna switches itself to the secondary node frequency and transmits the data. Wireless MIMO systems with multiple antennas employed at both the transmitter and receiver have gained attention because of their promising improvement in terms of performance and bandwidth efficiency [8].

Amateur Radio, better known as “Ham Radio”, is a hi-tech international hobby that exists for personal two-way communications, experimentation, and public service that is greatly enjoyed by people from all walks of life and all corners of the world. Ham radio has been referred to as “Old school” Communications since it has been around for over one hundred years and still going strong. It has also been compared by many as the Facebook, Twitter and the first wireless phone from the old days.

In MIMO system, let’s consider there is Mt transmitting antenna and Mr receive antennas where s= [S1, S2……SM] t is the transmitted data vector,

R G Gallager [1] in his paper, the overview of low density parity check codes are presented. The parity check matrix specifies these codes, which consists of few entries of non-zero elements. The number of non-zero elements in row should be greater than the number of non-zero elements in column. The typical minimum distance of these codes are directly proportional to block length for a fixed rate. A simple but non optimum decoding scheme operating directly from the channel is described. As block length increases, complexity of equipment and data

Multicarrier modulation provides immunity to fading caused by data transmission over mul-tipath fading channels or frequency- selective fading channels. Each of the subchannel expe-riences flat fading due to the decreased bandwidth. Also, due to the increase in the symbol period, it provides enhanced immunity to ISI. Another advantage of multicarrier modulation technique is it can provide better spectral efficiency compared to single carrier modulation, since the spectrum of the subcarrier can be overlapped.

The transmitter will weigh the transmission with weights, depending on the channelcoefficients, so that there is coherent combining at the single antenna receiver.The array gain in this case is called transmitter array gain. And vice versa for SIMO case, which will be known as receiver Array Gain. Basically, multiple antenna systems require perfectchannel knowledge either at the transmitter or receiver or both to achieve thisarray gain. Next important term is Diversity Gain. Multipath fading is a significant problem in communications. In a fading channel,signals experience fades.When the signalpower drops significantly, the channel is said to be in a fade. This gives rise tohigh bit error rates (BER).This involvesproviding replicas of the transmitted signal over time, frequency, or space. Thereare three types of diversity schemes in wireless communications:

Heterogeneous deployment need to use innovative cell association and inter-celling interference coordination techniques in order to realize the promised capacity and coverage gains. A typical heterogeneous wireless technology as shown in figure 1.4 has the

Selection combining is used fir very high frequency and ultra high frequency as maximum ratio combing and equal gain combing is not suitable to work under these high frequencies because tracking performance is not easy in a frequency changing or multipath fading. A simple implementation procedure is used in selection combining and is more beneficial then maximum ratio combining and equal gain combining. In this technique the highest signal level branch is selected. In short selection combining is used to look after all the diversity branches and

[1]S. M. Alamouti, describes a simple two-branch transmit diversity scheme. Using two transmit antenna and one receive antenna, the new transmit antenna provides the same diversity order as maximal-ratio receiver combining (MRRC) with one transmit and two receive antennas. The scheme easily be generated to two transmit antenna and M receive antenna to provide a diversity order of 2M. This scheme does not require any bandwidth expansion any feedback from the receiver to the transmitter and its computation complexity is similar to MRRC. This also provide diversity improvement to all the remote units in a wireless system, using two transmit antennas at the base station instead of two receive antenna at all the remote terminals.

4G is the integration of wireless LAN and Wide Area Network providing 100MHz for mobile and 1GHz for stationary devices. It uses packet switching networking and is based on Orthogonal Frequency Division Multiplexing Access (OFDMA) technology. Wireless LANs soon will begin multiplying or more in throughput and range if a smart antenna technology named MIMO works out as its benefactors foresee.

Antennas are key components of any wireless communication system and it is a device that provides a way for radiation or receiving electromagnetic waves. IEEE standard definitions for antenna (IEEE Std 145-1983) defines antenna as a means for radiating or receiving radio wave. Figure 3.1 shows an antenna as transition device. The arrows displayed in Figure 3.1 shows the electric field lines

Wi-Fi (ieee-802.11b) and Wi-Max (ieee-802.16e) have captured our attention. As there are no recent developments which transfer data at faster rate as video information transfer taking lot of time. This leads to introduction of Gi-Fi technology. It offers some advantages over Wi-Fi, a similar wireless technology. In that it offers faster information rate (Gbps), less power consumption and low cost for short range transmissions.

The characteristics of the channel satellite and mobile communications arm is an important and fast-growing wireless communications and play an important role in the transfer of information through the media of spread from the transmitter to the receiver with the minimum error rate.

We have introduced a new form of diversity for the concept of mobile communications system of cooperation. Cooperation by mobile phone users for each user is assigned. Cooperation can be considered as a new form of space diversity, antenna diversity in the transmission process, however, and other complications, Intermobiles noisy channels, each phone has sent a separate message. (W. Yu and T. Lan, 2007, pp. 2646–2660)