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Sam is a computer science student and working on a new micro robot design. The robot continuously sends every two seconds a status string comprising the accelerometer reading (4 bits), ultrasound obstacle detection (6 bits), motor functionality (4 bits) and battery power level (2 bits).
a) Calculate the data rate required for robot to remote controller communication
b) Explain 3 types of suitable encoding techniques could be used to encode the status string.
c) At a certain instance, the sensors provided data as acceleration 5 m/s2 obstacle at 48 cm, all motors working (i.e. motor functionality 1111), and battery is 75%.

i. Write the status string in binary for this instance
ii. Represent the status string on ASK, FSK, and PSK encoding techniques
d) Calculate the CRC for the status string derived in c) with polynomial divisor 11001101
e) Briefly explain some other error control and flow control techniques that Samcan use to ensure the accuracy of robot control.

Part II: Multiplexing and multiple access
Multiplexing plays an important role in communication as it allows the combination of multiple streams together. Different multiplexing techniques are used for various applications.
a) Explain TDM, FDM and CDMA multiplexing techniques with suitable diagrams
b) Main air interface in the change from 3G to 4G and WiMAX. Explain how
OFDM is different from above techniques and the special feature of signals used by OFDM
c) IEEE 802.11ac wireless LAN standard uses 40 MHz total bandwidth in OFDM scheme.

i. For 48 subscribers what should be the subcarrier bandwidth ( fb )
ii. Propose a suitable subcarrier bit time of T to achieve orthogonality
iii. Explain how OFDM overcomes the issue of inter symbol interference (ISI)

Part III: Wi-Fi
Prime Living is a real estate company based in Victoria and you work form them as a consultant network engineer. The company has decided to open a new office in South Eastern suburbs and the floor plan of the building is shown below. The office consists of 5 rooms and on average 8 employees work at each room. The lounge is used by both staff and customers and on average about 25 devices connect to Wi-Fi. The clients wants you to design the network for them with at least 100 Mbps data rate for all wireless connections. As resources you’ve got one distribution system and few access points of 10 m range.

## Data rate formula

The data rate formula is found by the number of bits that go through the network in bits per second

Bits sent=Sum of all each of the units=4+6+4+2=16 bits

The 16 bits have been sent in 2 seconds thus the number of bits in 1 second is given by

=16/2=8 bps

1. b) Explain 3 types of suitable encoding techniques could be used to encode the status string

One of the most likely important requirements for the design would be an encoding scheme with a high efficiency in terms of the bandwidth and higher effectiveness for the purposes of the wire communication  and thus the following could be treated as of higher efficiency in relation to encoding the bit strings (Jafarzadeh, Palesi, Khademzadeh, & Afzali-Kusha, 2014).

Everything kicks off at the start in NRZ-I encoding and is attained via turning to the opposite side when a 1 is obtained other nothing is done . Constantly attaining zeros translates to the same side remaining and nothing is changing(Ahmad & Habibi, 2008). An illustration of the same is as in the diagram below

Manchester Encoding

This makes use of different curves in demonstrating whether it is a zero besides another curve as shown below

ZeroOne

The ones encode greater voltages before using reduced voltages while the encoding of zero takes place with a high voltage before changing to low voltages. Illustrated in the diagram below is an example of the same

Differential encoding

Also called D-encoding, differential encoding works by generating an inversion up obtaining one input from a high to a low voltage and no inversions when a zero input is obtained as demonstrated in the diagram below.(Bakhurin et al., 2016)

1. C) At a certain instance, the sensors provided data as acceleration 5 m/s2 , obstacle at 48 cm, all motors working (i.e. motor functionality 1111), and battery is 75%.
2. Calculate the data rate required for robot to remote controller communication

The status string explains numerous individual bits that are delivered at an instant time. The first step in this determination is the conversion all the given values to a binary notation which would return 0101 which is a 4-bit data output.(Yan, ?ekercio?lu, & Narayanan, 2010)

The reading of the accelerometer is m/s2

Detection of an obstacle by an ultrasound takes place at 48 cm which upon conversion to binary notation returns

110000 which is a 6-bit input

The report of the motor status is provided in binary notation already which is 1111

The battery level is provided as 75%, in other words, 0.75 in decimal notation which when converted to binary notation returns 0.11 .

The array of each of the output data gives the aggregated status stream which is as illustrated

Status string=0101+110000+111+0.11 which returns

## Digital encoding techniques

0101110000111111 and hence the status string in the binary is given by

0101110000111111

1. Represent the status string on ASK, FSK, and PSK encoding techniques

In ASK the amplitude of the carrier signal is modulated going by the value of the data signal. A carrier signal is sent when a signal bit is transmitted. when a zero is transmitted there are no carrier signals meaning that the carrier signals can only be seen in cases where there is one digit signal and an absolute no visible signal upon the transmission of a zero. This is the underlying reason for ASK also being known as On-Off Keying. The diagram below illustrates the carrier wave.

Upon showing ASK, a wave as shown below is achieved

FSK

FSK uses two different carrier signals. The carrier frequency is changed from one frequency to a different frequency on sending logic one or zero  When the target  is sending logic one through FSK, logic one will be required to be transmitted on a specific carrier frequency while for the case of transmission of logic zero, the logic signals will need a transmission on a different carrier frequency(Liu et al., 2011). The diagram below illustrated the carrier wave.

After FSK, the signal is as shown

PSK

Changing the carrier signals phases enables sending of the message or data in PSK. In this technique, the digital signal is represented in a bipolar signal which is meant for two discrete values in the digital one and zero. There are two different poles: the 1 has a +ve pole while zero has a -ve pole. A change in the bit to be transmitted from logic 1 to logic 0 or logic 0 to logic 1 when the phase of the signal is changed by 180?. No changes to the digital input result to no changes to the carrier. The diagram below illustrates the wave diagram.

After PSK, the signal is as shown

1. d) Calculate the CRC for the status string derived in c) with polynomial divisor 11001101

CRC technique is applied in error detection in which the data and the divisor to be sent is given. The first step is to append a few bits, often zeros, to the data word bits . The appendage should be carried out in a manner that the number of zeros is one less than the bits number in the divisor

Data word=0101110000111111

Divisor=11001101 hence the number of zeros that are to be appended to the data word=8-1=7 zeros

The obtained CRC is then appended back to the word and a remainder of zero is to be attained. Basically, at the beginning, on dividing the word by the divisor and a non-zero and obtaining a non-zero remainder a conclusion is made that there was an error during transmission . When the reminder is zero then there wasn’t an error encountered during transmission (Nieto & Furman, 2009). Below is an illustration of the calculation

1. e) Briefly explain some other error control and flow control techniques that Sam can use to ensure the accuracy of robot control

## NRZ-I

Flow control

Flow control allows the sender to continually track the receiver and thereby the name closed loop protocol showing that the sender will continually be able to send packets only under situations that it is possible for the receiver to send it . The flow control methods suitable for the design of the robot include:

Sliding windows

This is a theoretical concept implementable through the following mechanisms

GBN (Go Back N)

The main underlying concept behind this scheme is the adoption of sliding window which allows the sender to send files without having to receive acknowledgements even though immediately the source realizes failure of reception of one of the frames or the frames being received in a gabbed form, resending will be done to not only that particular frame but also to the subsequent frames. This concept remains even if the destination received some of such frames . Among the critical aspects in the Go Back and N design encompass a larger than one size of the window sender in going back N. In case it is one then it would literally be just a mere stop for the protocol and would be meaningless (Yao, 1995). The figure below illustrates the concept

Stop and Wait for flow control

The Stop and Wait for flow control is one of such simple forms of flow control and encompasses the sender sending the first frame which will then be received by the receiver. Upon the receiver processing frame number one, a request will be sent for frame number two through sending an acknowledgment number 2 which would then be sent by the sender and received by the receiver.

Frame number three is sent in a similar way along the subsequent frames that are to be sent  The key concept behind this is that a packet is released by a sender and then stops and waits until a receipt of an acknowledgment note from the receiver indicating it has finished processing the frame and hence another frame may be sent. The advantages among the being simple to design make it have higher scores in the design of the robot . Shown below is a summary of the concepts in diagram form(Thomas, Sharma, Banerjee, Lee, & Dalal, 2013)

The main drawback with the technique is the delay time in the sending of an acknowledgement which further lowers the efficiency of the method.

Error control techniques

## Manchester Encoding

A channel is needed for the transmission of data from a transmitter to the receiver and such a channel is susceptible to addition of noise to the data that is being sent (Swenson & Bhandari, 2014). The result will be a distortion of the data hence the need for error detection and correction in data communication

Error control methods:

Hamming code

In most practice, 7-bit Hamming code is adopted and the following are the general provisions in getting the bits:

The parity and data bits are sent at the same time, the parity bits detect errors. An example is when the a data bit of 4 and a parity bit of 3 are sent, a Hamming code of 7 units is achieved

Make a choice on the data bits position and the parity bits position which is achievable through the following mechanism(Etzion & Silberstein, 2008)

2n {where n=0, 1...n} will be the position of the parity bits

D4                    D3                    D2                    p3                     D1                    p2         p1

7                      6                      5                      4                      3                      2                      1

20=1 (Position 1 is parity bit)

21=2(Position 2is a parity bit)

22=4(Position 4 is a parity bit)

23=8(Position 8 is a parity bit but which is not available in practice)

The remaining positions would be occupied by data bit . A Hamming code arrangement like the above is sent to the receiver to carry out an evaluation for detection of error through finding whether the bits are odd or even as provided by the parity bits.

Backward error control

FEC is a mechanism of enhancing the performance of the link where the receiver can check and detect an error thereafter sending the information to the sender for so as to retransmit the frame via the process called automatic repeat request.

Forward error control

Forward error control tends to be more of data received contrary to as to data retransmission. On detecting the error through using different algorithms, the different additional bits values parity bits are used by the receiver in performing error detection .The algorithm adopts the principle of Hamming distance to establish the probability of making a correction to the error by the bit flip(Luby, Watson, & Shokrollahi, 2010).

## Differential Encoding

II: Multiplexing and multiple accesses

Each radio spectrum has a limited bandwidth which needs to be accessible to all the subscribers for use. Multiplexing allows abundant mobile users to have access to the narrow spectrum.  Below are the various techniques

1. a) Explain TDM, FDM and CDMA multiplexing techniques with suitable diagrams

FDMA is a multiplexing technique which allows all users to gain access to and simultaneously use the same band frequency. A base station has the capability to engross users at the same time using diverse frequencies .Possibilities of hindrance when frequency slots are adjacent to each remain as the outstanding drawback of this set up. This is checked by assigning a guard band to every frequency slot. The guard bands do not participate in the transmission of data. An illustrative diagram is as shown below

TDMA

This technique divides the users in relation to the time slot such that every user is able to access the band frequency even though at unalike time intervals (Elliott, 2011). This set up requires a suitable synchronization with the transmitter and this tends to be the main challenge. The diagram below is an illustrative diagram

CDMA

This method encompasses the apportionment of an exceptional sequence to a user and the encoding of the user data with the aid of the transmitter using its unique code and then decoding of the data by the receiver by the unique code for the explicit user(Palanki, Khandekar, & Sutivong, 2014) . The CDMA technique adopts spread spectrum algorithm with every of the users in CMDA having an access to an explicit code known as chipping sequence. The code is orthogonal meaning that multiplying the codes together returns a zero. Spreading which defines the process of multiplying the code with the data transpires at the transmission point and the data alongside the code are transmitted together. The reverse process, de-spreading transpires at the receiver in where the received signal input is multiplied by the receiver. (Choi, Ho, Liu, & Hui, 2010).

1. b) Main air interface in the change from 3G to 4G and WiMAX. Explain how OFDM is different from above techniques and the special feature of signals used by OFDM

The orthogonal frequency division multiples access exhibits the same properties as the traditional frequency division multiples access only for the carrier which are generated by a single transmitter  in an explicit manner which allows them to be squeezed adjacent to each other as well as span a comparatively greater bandwidth of up to 200 MHz making it a possibility to lower or totally remove the use of guard bands and thereby allow packing of more bits per hertz hence improving the efficiency with a lot of alteration in the existing system (Maccartney et al., 2015). This has been achieved through specific properties in OFMD among them OFDMA subcarrier signals which are pulses in rectangular shape in the time domain. Such subcarriers signals tolerate sine (f)/ (f) or sync (f) in their frequency domain. Such a set make improvement in the achievement of orthogonality hence does cause hindrance with each other. (Glisic & Leppänen, 2012)

1. C) IEEE 802.11ac wireless LAN standard uses 40 MHz total bandwidth in OFDM scheme.
2. For 48 subscribers what should be the subcarrier bandwidth ( fb ) ?

FO=B/N

Fo= Fundamental frequency

B=The total bandwidth

N=Total number of subcarriers

Fo=?

B=40

N=48

B=Fo/N

=40/48

=0.833MHz

= 833 KHz

1. Propose a suitable subcarrier bit time of T to achieve orthogonality

T=1/B =1/0.833

=1.2s

iii. Explain how OFDM overcomes the issue of inter symbol interference (ISI)

OFDM signal is opportunistic of the property of orthogonality which allows terms closely be packed to each other without of the ISI issue which leads to elimination of the use of guard bands in minimizing orthogonality (Hwang, Yang, Wu, Li, & Li, 2009).

Part III: Wi-Fi

1. a) Design the network specifying the locations of access points and distributions system showing the backbone network.
2. b) Calculate the BSS and ESS sizes

BSS=Area covered by each Wi-Fi hotspot

Rm 1 Area=L*W=10*10=100m2

Rm 2 Area =L*W=10*10=100m2

Rm3 Area =L*W=10*10=100m2

Rm 4 Area =L*W=10*10=100m2

Rm 5 Area = L*W=10*10=100m2

Lounge Area =L*W=20*10=200 m2

ESS=Set of all the area covered by the individual Wi-Fi access points

= (100+100+100+100+100+200) =500+200=700m2

1. c) Calculate the throughput for the DS

Throughput=Sum of individual throughput

8*100=800(Individual room throughput)

For five rooms=5*800=4000

Plus the lounge 25*100=2500

Total throughput =4000+2500=6500mbps

1. d) Recommend a suitable IEEE substandard for the network and give reasons for your choice

802.11ac would be the most suitable IEEE substandard network as it provides higher data rate alongside a great number of users for each channel band in comparison with the earlier standards which just offered a limited number of active connections .(Ong et al., 2011)

1. e) Recommend suitable security strategies for the network
• Adopting a strong password that guarantees the security and encryption of each network
• Enhancing the data security when in transit through WPA2 wireless encryption standards. WPA2 id advantageous in the sense of less vulnerability relative to WEP and WPA
• Turn on the WPS convenience button when using a business network.

References

Ahmad, I., & Habibi, D. (2008). A proactive forward error control scheme for mobile WiMAX communication.

Bakhurin, K. I., Goudar, V., Shobe, J. L., Claar, L. D., Buonomano, D. V., & Masmanidis, S. C. (2016). Differential encoding of time by prefrontal and striatal network dynamics. Journal of Neuroscience, 1789–16.

Choi, W. P., Ho, W. C., Liu, X., & Hui, S. Y. R. (2010). Bidirectional communication techniques for wireless battery charging systems & portable consumer electronics. In Applied Power Electronics Conference and Exposition (APEC), 2010 Twenty-Fifth Annual IEEE (pp. 2251–2257). IEEE.

Elliott, B. B. (2011). Time division multiple access for network nodes with multiple receivers. Google Patents.

Etzion, T., & Silberstein, N. (2008). Error-correcting codes in projective spaces via rank-metric codes and Ferrers diagrams. ArXiv Preprint ArXiv:0807.4846.

Glisic, S. G., & Leppänen, P. A. (2012). Code division multiple access communications. Springer Science & Business Media.

Hwang, T., Yang, C., Wu, G., Li, S., & Li, G. Y. (2009). OFDM and its wireless applications: A survey. IEEE Transactions on Vehicular Technology, 58(4), 1673–1694.

Jafarzadeh, N., Palesi, M., Khademzadeh, A., & Afzali-Kusha, A. (2014). Data encoding techniques for reducing energy consumption in network-on-chip. IEEE Transactions on Very Large Scale Integration (VLSI) Systems, 22(3), 675–685.

Liu, X., Chandrasekhar, S., Wood, T. H., Tkach, R. W., Winzer, P. J., Burrows, E. C., & Chraplyvy, A. R. (2011). M-ary pulse-position modulation and frequency-shift keying with additional polarization/phase modulation for high-sensitivity optical transmission. Optics Express, 19(26), B868–B881.

Luby, M. G., Watson, M., & Shokrollahi, M. A. (2010). Forward error-correcting (FEC) coding and streaming. Google Patents.

Nieto, J. W., & Furman, W. N. (2009). Cyclic redundancy check (CRC) based error correction method and device. Google Patents.

Ong, E. H., Kneckt, J., Alanen, O., Chang, Z., Huovinen, T., & Nihtilä, T. (2011). IEEE 802.11 ac: Enhancements for very high throughput WLANs. In Personal indoor and mobile radio communications (PIMRC), 2011 IEEE 22nd international symposium on (pp. 849–853). IEEE.

Palanki, R., Khandekar, A., & Sutivong, A. (2014). Code division multiplexing in a single-carrier frequency division multiple access system. Google Patents.

Thomas, D. A., Sharma, P., Banerjee, S., Lee, S.-J., & Dalal, A. C. (2013). Method and system for content downloads via an insecure communications channel to devices. Google Patents.

Yan, X., ?ekercio?lu, Y. A., & Narayanan, S. (2010). A survey of vertical handover decision algorithms in Fourth Generation heterogeneous wireless networks. Computer Networks, 54(11), 1848–1863.

Yao, Y.-D. (1995). An effective go-back-N ARQ scheme for variable-error-rate channels. IEEE Transactions on Communications, 43(1), 20–23.

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