Abstract
Wireless networking involves connecting network nodes using wireless data connections in the network. Wireless networking enables people to save on the costs they would have incurred in bringing in cable to their houses or offices. Some wireless networks include terrestrial microwave networks, Wi-Fi local networks, and cell phone networks. Examples of wireless methods include TDMA, PTP, and PTMP. This research paper looks into TDMA, PTP, and PTMP. It also looks at other elements involved in the wireless network such as 2.4 GHz, 5GHZ, and Fresnel Zone.
Introduction
Wireless networking involves connecting network nodes using wireless data connections in the network. Wireless networking enables people to save on the costs they would have incurred in bringing in cable to their houses or offices. Radio communication administers and implements networks of wireless communications. Implementation of the wireless network occurs on the physical level of the OSI model. Some wireless networks include terrestrial microwave networks, Wi-Fi local networks, and cell phone networks. Examples of wireless methods include TDMA, PTP, and PTMP.
TDMA refers to Time Division Multiple Access. It is a method that enables the accessibility of channels in shared networks (Linnartz, 2014). TDMA enables multiple users to share a channel through the division of the signal into time slots. Users are able to transmit their data at the same time due to the accessibility of their own slots. TDMA enables many stations to share a transmission medium. A good example is the radio frequency channel. TDMA is also used in the 2G cellular systems. Examples of these 2G cellular systems include Personal Digital Cellular, IS-136, Global System for Mobile Communications, and iDEN. TDMA is also used on portable phones through the Digital Enhanced Cordless Telecommunications. TDMA is used in combat-net radio systems, PON systems, and satellite systems (Eidson, 2010). The PON networks connect the operators to the premises in an upstream traffic.
TDMA divides the cellular channels into 3 slots so as increase the data being transported. TDMA has multiple transmitters connected to a receiver (Rouse, 2013). The feature of connecting several transmitters to one receiver becomes difficult in cases of mobile phones where the phone moves further away from the base station. The movement of the device makes the advance timings difficult to match up with the gap created during transmission (Rouse, 2014). TDMA has several characteristics that make it useful to the users. It has the ability to enable sharing of a frequency among multiple users. The slots created by TDMA can be assigned to users based on their demand. The system becomes simple because of transmission that is non-continuous. There is less cell interference while using TDMA; therefore, the power control is less stringent compared to CDMA. TDMA has a high overhead on synchronization. TDMA has a complicated cell breathing process. The process of allocating frequency to slots is complex. TDMA interferes with other devices due to its possession of pulsating power (Eidson, 2010). TDMA can also cause inter-symbol interference if the frequency is highly selective. TDMA will be required to use advanced equalization if the rates of data are high.
TDMA is used in the systems of mobile phones. These systems include 2G systems, and 3G systems. A majority of 2G systems use TDMA except IS-95. Examples of 2G cellular systems that use TDMA include GSM, PDC, D-AMPS, PHS, and iDEN. GSM minimizes interference by combining TDMA with wideband transmission and frequency hopping (Eidson, 2006). GSM achieves synchronization of phones through sending commands from the station instructing the phones on early transmission and the quantity of transmission (Whalen, 2009). Early transmission makes up for the delay caused by low speed of radio waves. The phones are not allowed to transmit to their whole slots; however, a guard interval is present at the end of each slot of time. During the guard interval the timing can be adjusted so as to enable the synchronization of transmission.
Care should be exercised during the first synchronization of a mobile phone. At the initial stage, the network is not able to tell how much is required by the phone to necessitate an adequate transmission (Eidson, 2006). The phones are, therefore, a whole time slot is prepared for those mobile phones that are trying to connect to the network. That kind of process is called the random access channel (RACH). The mobile phone tries to transmit at the start of the time slot. Nearness to the base station will prevent delays, and enable the transmission to be a success. In cases where the mobile phone is farther away from the base station by less than 35 km, there will be delays (Eidson, 2010). The transmission will arrive towards the end of the time slot. The mobile phone will, therefore, be sent instructions to send the transmissions earlier. If the distance between the mobile phone and the base station is more than 35 km in GSM, the transmission will end up arriving in another time slot and will be ignored. That characteristic of GSM limits the mobile phones to 35 km when there are no extra reinforcement techniques that have been put into place. The limitation can be reduced through changing the synchrony existing between the downlink and uplink in the base station.
A majority of 3G systems are based on CDMA, but there are a few that use the combination of TDMA and CDMA. Examples of such systems include dynamic TDMA, packet oriented multiple access schemes, and TDD (Linnartz, 2014). These systems combine both TDMA and CDMA so as to benefit from the advantages of these different technologies. TDMA is also combined with TDD and CDMA in the use of UMTS UTRA (Linnartz, 2014).
TDMA is used in radio systems together with FDMA and FDD. The combination of the three methods is known as FDMA/TDMA/FDD. Such a combination is available in both IS-136 and GSM. PHS, DECT, TD-SCDMA, and UMTS-TDD use the time division duplexing. In the time division duplexing, the various time slots of handsets and base station are allocated on a common frequency.
TDMA has an advantage because the mobile phone’s radio broadcasts at its time slot. The remainder of the time can be used by the mobile phone in measuring the network, and detection of neighboring transmitters that are on other frequencies. The positive factor about this characteristic is that it promotes inter-frequency handovers that are safe. CDMA systems are not able to do this function. IS-95 does not support this function at all. UMTS can manage, but it will require the addition of complex systems. These additions demand that microcell layers co-exist with macrocell layers. CDMA enables the mobile phones to communicate with 6 base stations at the same time (Eidson, 2010). It contains the feature of same-frequency handover. The packets that are incoming are checked in terms of quality, selection of the best packet is made. The cell breathing feature of CDMA can hinder the execution of the same-frequency handover when it is peak period. The boundaries of the two cells are unable to get clear signals; therefore, there is no smooth flow during handover.
TDMA systems have disadvantages because the system causes frequency interference where there is a connection to the length of the time slot. The phone can cause a buzz sound if left near a speaker or radio (Whalen, 2009). TDMA also has a disadvantage based on the dead time that exists between two time slots. The dead time puts a limitation on the bandwidth of the TDMA channel. The effect of this limitation is that implementation is done in parts because it becomes difficult to ensure that the terminals will transmit at the times they are required to do so. The mobile phones that are in movement will keep on adjusting their time slots so as to ensure that their transmissions are received at the expected time. The further the phones move away from the base station, the longer it takes for the transmissions to arrive. The TDMA systems experience hard limits on sizes of cells because of range. The powers needed to transmit and receive over distances that are longer than the distance that is supported are usually not practical.
Dynamic TDMA uses scheduling algorithms to reserve several time slots (Eidson, 2010). The time slots are reserved in form of bit-rate streams of data that vary. The demand for traffic on the data streams determines the time slots that will be reserved. There are several systems that use the dynamic TDMA. These systems include IEEE 802.16a, Ubiquiti airMAX, Bluetooth, PRMA, Intelbras WISP+ Radios, HIPERLAN/2, ITU-T G.hn, and TD-SCDMA.
PTP
PTP is known as Point-to-Point and is used in wireless communications. PTP connects two regions by through the formation of an Ethernet bridge. The two areas have a distance of several kilometers between them. There are several suggestions on what distances the PTP should cover. The real distances are, however, affected by factors such as environmental interference, EIRP, Line of Sight, and many other factors. The products that are recommended are based on distances (Ubiquiti, 2014).
Short distances are approximated as ranging between 0 and 5 km. Examples of PTP products that fall under the short distance includes Loco M, and Nano M. Loco M is best for links that have very short distances. It is one of the PTP solutions that have very low costs. The Nano M is popular for short links. It is used a lot in video surveillance because it has a dual Ethernet port (Ubiquiti, 2014).
Medium distances are approximated as ranging between 5 and 15 km. Examples of PTP products that fall under this category include airGrid M, NanoBridge M, and PowerBridge M. AirGrid M are used in low links (Ubiquiti, 2014). The focus of airGrid is more on wind-loading properties, low prices, and connectivity. Performance is not a priority in this PTP product. The NanoBridge M focuses on links that have medium level distances. It upholds performance of the protocol. The PowerBridge M focuses on those links that are between medium and long distances. It has a large memory compared to the other products so as to raise the performance level.
The long distances are approximated to be 15 km and above. An example of the PTP product under this category is Rocket M w/Dish. The Rocket M w/Dish focuses on high performances of the PTP links in the industry. It produces 150Mbps TCP/IP throughput. The product can also cover distances above 100 km.
There is another category of products that focus on high performance. An example of a PTP product in this category is the airFibre 24. The airFibre 24 is used to promote exceedingly high performance. It delivers actual throughput of 1.4Gbps in distances of more than 5 km under the band of 24GHz. There are certain situations where this product can be used for distances that reach 13 km (Ubiquiti, 2014).
PTMP
PTMP is known as Point-to-Multipoint. PTMP creates a connection between three and above regions. PTMP utilizes base station and CPE devices to connect to the Access Point. The performance of the PTMP depends on the two sides of the link. It is therefore very important to choose the correct CPE and the correct Base Station for every case. Correct selection will enable the data to reach long distances (Ubiquiti, 2014).
The Base Station is normally located at a high region. It could be on top of a building, tower, or mast. The height at which the base station is located determines the maximum level of coverage the PMTP will cover. At the planning stage, it is advisable to plan with an antenna that has a low coverage, and will still be able to cover the targeted area (Ubiquiti, 2014). The antennas that have a beam-width that is wider will be able to cover a larger zone and reach many stations, but they are more likely to be faced with interference. Interference will lead to decrease in performance and scalability.
The base stations are categorized into two types. The first category is the low capacity and short distance base station. It is more suited for beginners, and for areas that do not have a lot of interferences. The second category is the high capacity and high performance base station. It focuses on a wider coverage, and aims at high performance.
The low capacity and short distance base station is encouraged for people who are starting up. An example of a product under this category is Rocket M with Rocket-OMNI antenna. The product covers around 60 stations that are concurrent (Ubiquiti, 2014). The product is highly prone to interference and is recommended for areas that highly or moderately rural.
The high capacity and high performance base stations have products that seek to have wide coverage and increase performance. Examples of these products include Rocket M with Standard Sector Antenna, and Rocket M-Titanium and Titanium Sector Antennas. Rocket M with Standard Sector Antenna meets the standards set by the industry for base stations. The product contains either three 120o antennas or four 90o antennas for coverage of 360o. Each product covers 300 stations per base station (Ubiquiti, 2014).
The Rocket M-Titanium and Titanium Sector Antennas provide high performance in areas that have high density. The beam-width is variable and ranges between 60o and 120o antennas so as to promote scalable growth. Each base station covers 500 stations. The product has added technology that helps in avoiding interference based on location. These technologies include airSync technology and superior isolation technology (Ubiquiti, 2014).
CPE is known as Customer Premise Equipment. The CPE devices must link correctly with the base stations so as to reach long distances. The CPE devices are also categorized in terms of distances to be covered. There categories include short distance, medium distance, and long distance. Short distance includes products such as Loco M, and Nano M. Medium distance includes products such as airGrid M, and NanoBridge M. Long distance include products such as PowerBridge M, and Rocket M with RocketDish.
The short distance covered is approximated to be between 0 and 3 km. The product Loco M covers a very short range, and has the lowest cost. It is considered to be a CPE that is the least directive (Ubiquiti, 2014). The product Nano M has a bigger range compared to that of Loco M. It is considered to have a greater directive as compared to Loco M.
The medium distance CPEs cover a distance between 3 and 7 km. The product airGrid M is considered as a low cost CPE. The width of the beam is very narrow, but it can still give a high performance. The product NanoBridge M is considered as a CPE that is highly directive. It covers a range that is bigger than that covered by airGrid M. The noise produced by the product is lower compared to that produced by airGrid M.
The long distance CPEs cover longer distances than the two previous categories. The product PowerBridge M is a device that has high power. The CPE is highly directive, and covers a longer distance compared to the other CPEs in the other categories. The noise produced by the product is very low. It also possesses an aesthetic beauty that makes it more attractive than the dish (Ubiquiti, 2014). The product Rocket M with RocketDish is the CPE that has the highest performance compared to the other CPEs. It incurs a high cost because of the array of designs that are carefully integrated. Most people can fail to recognize it as a CPE.
High performing devices can be used for shorter distances because they will perform better than the devices intended for such distances. An example is where a PowerBridge M is used in short distances instead of Loco M. The PowerBridge M will perform better than the Loco M because of the properties that the antennas possess.
2.4 GHz Wireless
2.4 GHz indicates the frequency of the waves that the base station sends to devices. There are several bands surrounding 2.4 GHz that have been assigned to medical, scientific, and industrial bands (Herman, 2010). The advantage of 2.4 GHZ is that you do not need a license to use them. 2.4 GHz has several disadvantages such as restriction to three 2oMHz channels that do not overlap; channels of 40 MHZ are not allowed; and the band is crowded thus suffers a lot of interference.
5 GHz Wireless
5 GHz indicates the frequency of the waves that the base station sends to devices. 5 GHz can be used worldwide without the need for licensing. It also allows for high limits of EIRP leading to connection of links that are long distance. It can also allow more antennas to gain access to the system. 5 GHz enables large amounts of data to be transmitted, and makes it easier to locate the devices that are near (Mitchell, 2014). The disadvantage of 5 GHz is that it has a weak propagation and low frequencies in situations where there are obstacles.
Wireless Fresnel Zone
The Fresnel zone refers to the area that surrounds the link of the line of sight. The line of sight needs to be protected from obstacles that are likely to cause reflections. The reflections can decrease the quality of the signal. Below is a diagram showing the Fresnel zone.
References
Rouse M., (2014). TDMA (Time Division Multiple Access). Retrieved from: http://searchnetworking.techtarget.com/definition/TDMA
Herman J., (2010). Why Everything Wireless is 2.4 GHz. Retrieved from: http://www.wired.com/2010/09/wireless-explainer/all/
Mitchell B., (2014). Is 5 GHz Wi-Fi Network Hardware Better than 2.4 GHZ. Retrieved from: http://compnetworking.about.com/od/wirelessfaqs/f/5ghz-gear.htm
Ubiquiti, (2014). Getting Started with AirMax. Retrieved from: http://wiki.ubnt.com/Getting_Started_with_airMAX
Linnartz J. P., (2014). Time Division Multiple Access (TDMA). Retrieved from: http://www.wirelesscommunication.nl/reference/chaptr04/multi/tdma.htm
Whalen J., (2009). Minimize GSM Buzz Noise in Mobile Phones. Retrieved from: http://www.eetimes.com/document.asp?doc_id=1276434
Eidson J., (2010). IEEE 1588 Standard Version. New Jersey: Prentice Hall
Eidson J. C., (2006). Measurement, Control and Communication Using IEEE. New York: Wiley
