The paper “Multi-Hop Wireless Networks” is an engrossing example of coursework on information technology. WLAN is the current technology of communication that is being adapted almost by all sectors such as schools, businesses, large organizations among others. The frequencies that transmit data from one source to destination are exposed to Radio Frequency (RF) interface by nature from different sources. This frequency band is unlicensed hence the growing number of users which makes it overcrowded (Akella, 2005). The range of devices such as cordless phones, Bluetooth headsets, ‘ WirelessUSB’ peripherals which operate in 2.4GHz band is on the 802.11b/g networks (http: //tinyurl. com). Multipath propagation is where the signals from the source to destination take different channels or paths (Geier, 2002).
The signals travel through a medium with many obstacles such as the wall, seats, and other items which may cause the signal to bounce in various directions. A signal transmitted from the source and bounces in many directions reaches the destination at different times. Some signals may be distorted along the way or lost signal strengths. The received signal causes misrepresentation of symbols in the 802.11 signal where signals overlap due to delays from the multipath.
The receiver demodulates the signal received which is a wrong representation from the original signal. Hence wrong information is decoded. Inter-symbol interference is where the symbol representation overlaps. Sometimes earlier arriving signals and delayed signals may have the same strength but out of phase hence cancels each other and there is nothing received. The destination will detect the errors in the received data by checking the checksum which will not add up. This causes the destination not to send an acknowledgment message to the source.
The source will resend the packet if the time for receiving acknowledgment elapses. This retransmission reduces the users’ throughput. Antennas have been used to boost the signals after losing energy along the way as they pass through obstacles. But it is hard to overcome some challenges of multipath problems such as canceling out of the signals at the destination. The rake receiver has been used to overcome this problem where it holds every delayed multipath carrier. The rake receivers become ineffective if the multipath signals are completely distorted or strongly canceled each other rendering the rake receiver with on carrier to lock on to.
Military GPS receivers are mitigation for a multipath problem where the beams are directed to a satellite. This receivers uses adaptive beamforming and nulling antennas to overcome the multipath problems and improve the throughput of WLAN by ensuring that there will be retransmission. Purposes of POE in WLAN design
Power over Ethernet (PoE)
This is a technology for Local area network (LAN) wired Ethernet which reduces the number of cables needed while installing LAN where the power which is required by the device to operate is supplied by data cables instead of power cables or cords.
It is important to determine if a given switch can supply power to an access power via PoE by considering the amount of power required by the access point.
- A. Akella, G. Judd, S. Seshan, and P. Steenkiste(2005), Self management in chaotic wireless deployments. In MobiCom
- Bluetooth coexistence with 802.11, retrieved from ,http://tinyurl.com/2grndv
- M. Kodialam and T. Nandagopal. (2003), Characterizing achievable rates in multi-hop wireless networks: the joint routing and scheduling problem, In MobiCom
- T. Karhima, A. Silvennoinen, M. Hall, and S.-G. Haggman ( 2004), IEEE 802.11b/g wlan tolerance to jamming. In MILCOM