MITS5003 Wireless Networks And Communication

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).

Wireless communication according to Elgal,Mesleh and Haas(2011) documents that wireless communication is the future of the world in the communication arena in the realization of global village aspect of technology as the driver.

1. Calculate the data rate required for robot to remote controller communication.

Data rate in other words implies the bandwidth or the frequencies that can pass through a medium .

Accelerometer – 4bits

Ultrasound obstacle detection -6bits

Motor functionality -4bits

Battery power level -2bits

  2(battery power level)*4(motor functionality)/accelerometer reading(4)*obstacle detection(6)

  2*4/4*6=0.3Hz. 

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

To encode means to put a sequence of characters into a specialized digital format for efficient and effective transmission, the suitable encoding techniques would be;

NRZ ENCODING-stands for non-return to zero research by Lu,P,Xu., and Liu ,X(2013) reported  that it is the common and easiest way of transmission of digital signals. NRZ encoding uses two distinct voltage levels as the signal details of the duo binary digits. It is used for both synchronous and asynchronous communication. The uniqueness of NRZ is that it only encodes positive and negative signals and never will encode zeros.

Research by Roufa,Mustafaa , Tylora,Xua,Gruteserb,Trappeb and Serskab(2010) documented that Manchester Encoding-Is a synchronized encoding category normaly used by physical layer to take in the synchronized bit stream, the binary data channeled over the cable are not sent as a series of 1s and 0s.

NRZI ENCODING-stands for non-return to zero inverted encoding. It is majorly used in telecommunication transmissions in which a bit of data of 1 is a positive voltage while a bit of data of 0 is a negative voltage. NRZI singles binary signals to eminently physical hints in the channeling. If a bit of data is 1, NRZI changes at the clock interface. On the other hand if a data bit is 0, there is no change. NRZI at times have long sequences of 0s or 1s, culminating into clock recovery hitches. 

1. 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%.

Write the status string in binary for this instance.

Acceleration -0101

Obstacle – 0100 1000

Battery  -0111 0101

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

ASK:

S(t) = { A0,cos(2pieFct), binary 0,

             A1,cos(2pieFct),binary 1

FSK: 

S(t) = AcCos(2nfct + Df intergral subscript negative infinity    superscript  t m(theta)d theta)

Ac = amplitude of CPFSK

fc=base carrier frequency

Df=parameter for frequency deviation.

Intergral gives the signal its continuous property.

             n=pie

              t=time

             d=differential 

PSK:

In PSK two phases represents two binary digits.

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

G(x),M(x) as bit sequence  of coefficients 0 and 1

  ^{y4 + y3 +y2 +1.}

 _{An An+1 An+2 as the message}

_{bits: B(y) = An}^{yn +}A_n+1^y+1 +A_n+2^yn+2

y^kB(y) = Q(y)G(y) + R(y)

x^kB(y) + R(y)

//addition and subtraction are same at mod 2

Hence  Y^kB(y) – R(y)

11001101 is of degree 3.

Y^{7 +} y⁶  + y⁴ + y² + y +1

Y⁷ + y² + 1/y³ +y² +1) y¹⁰+y⁹ +y⁷ + y⁵  +  y⁴ +y³

                                      Minus  Y¹⁰  +  y⁹ +y⁷   

                              Y⁵ + y⁴ + y³

                              minusY5 ⁺ y⁴ +y2

                                  y³ + y²

                      minus y³ + y² +1

   Ans=1

1. Briefly explain some other error control and flow control techniques that Sam can use to ensure the accuracy of robot control.
2.  

Okamura,Murakami  and Orihansh.(2013) found that it is a linear forward error correcting code which yields parity symbols by convolving a data stream with generating sequences as called .It can be modelled as a finite state markov state chain that gives a graphic representation known as the state diagram.

Li and Singh.(2010) records that In rate-based flow control mechanism, each node is given a maximum rate and an average rate of transmission .The commonly used method of flow control is biult on windows, in which the rate at which a source sends packets relies on both the size of a window and on the rate of reply from the network to the origin. On high-speed networks, the round trip postponement from source to an intermediary node and back is relatively high in relation with packet transmission times, so that the windowing method does not react quickly enough to deter congestion and  delays. Also, high-speed networks requires to accommodate a wide scope of source transmission speeds and windows do not perform very well under such situations.

In this t technique the recipient ilgives an indication of it's readiness to take in data for every time,the message is packed into frames and the sender must wait for an acknowledgement.

Fb=N/2*delta_f where delta_f is the subcarrier frequency spacing.

d_f=1/Ts where Ts is the duration.

48/2*1/Ts is the fb.

(ii) suitable subcarrier bit time.

Using appropriate algorithm:

SA=(X,X_2,X....X-1,X,1,X-2...)

Bit value confined between 0-N thus appropriate rate=0<=c<=N

(iii) Explain how OFDM overcomes inter symbol interface, it is a propagation error which arises from multipath signals formally known as noise.The common mitigation technique is the use of adaptive equalizer.

Uqualization method,this is an equalizer that auto adapts to time variant traits and usually used with coherent modulation techniques like the PSK.

Multiplexing plays an important role in communication as it allows the combination of multiple streams together. Different multiplexing techniques are used for various applications.

Chang and Cheng.(2011) found out that TDM also known as Time Division Multiplexing in full is a technique of conveying and receiving sovereign signals over a mutual hint path by means of harmonized switches at each end of the broadcast line so that each signal seems on the line only a segment of time in an discontinuous pattern. It is used when the bit rate of the transmission channel exceeds that of the signal to be transmitted.

FDM also known as Frequency Division multiplexing is a technique in which many hint signals are joined for transmission on a single communication channel. Each signal is assigned to a unique frequency within the major channel and requires to be harmonized. The channel should have a good bandwidth to be able to take in a range of frequencies. 

CDMA is also referred to as Code Division Multiplexing Access, it is a method by which numerous data signals are combined for concurrent broadcast over a mutual frequency band.

When CDM is employed to allow multiple users to share a single communications channel, the technology is known as Code Division Multiple Access (CDMA).  

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 

Zheng,(2010) found out that air interface generally is a communication link between stations in mobile, it is radio based in which a subscriber navigates  from one cell to another in the system. As this takes place, there is a periodic change in the active base and each change is called handoff. 

Cho, Kim,Yang and Kang.(2010) found that OFDM also known as Orthogonal frequency division multiplexing uses a digital multi carrier modulation technique. Li,(2010) found out that the main difference between OFDM and main air interface is the fact that main air interface involves handoff while OFDM uses digital multi carrier instead of the handoffs. 

802. IEEE 802.11ac wireless LAN standard uses 40 MHz total bandwidth in OFDM scheme.

It is a set of media access control and physical layer control layer specifications for (I) subcarrier bandwidth for 48 subscribers.

 LAN and in OFDM it states that the frequency used must be 40 Mega Hatz. 

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 10m range. 

a.Network design.

  Designing the network using the enterprise campus architecture with three subnets A,B,C 

core Layer      / distribution layer.  

1. Calculating the BSS, bss is the common access point of the two networks,ess on the other side is the effective sample size.

Ess=1/n intergral of i=1 to n*y  

1. calculating throughput for DS.

Differentiated Services  DS  is a protocol for showing and controlling network traffic by class.

DS= bandwidth/nodes. 

1. Recommend a suitable IEEE substandard  for the network  and give reasons. 

I would recommend IEEE 802.2 as the substandard for this network , it is responsible for data link that are sovereign of the underlying medium thus makes it suitable for this network.

1. Recommend security strategies. 

  Coming up with safety put ups would necessitate one to have in mind the safety loopholes that the network might encounter. In this scenario the internet safety is the key issue to take into consideration.

An entry guideline that defines entry permissions and preferences. The entry guideline must give guidelines for connecting external networks, connecting devices to a network, and adding new programs to program. An entry guideline may also guide on how data is grouped for instance, private, internal, and top privacy for that matter.

A responsibility entry that shows the obligation of users and management. The obligation guideline should single out an audit capability and provide incident-handling guidelines that stipulates what to do and whom to contact if a possible intrusion is detected.

Access guideline that sets up trust by an effective password policy and sets up steps for not onsite location authentication.

A privacy guideline that dictates reasonable expectations of privacy concerning the overseeing of email, logging of keystrokes, and entry to files. 

Safety procedures done on safety policies. Guidelines define set up, entry, audit, and maintenance procedure. Safety procedures are written for end users, network admins. Safety procedures should single out how to tackle incidents  

Lu, P., Xu, Z., Lu, X., & Liu, X. (2013). Digital image information encryption based on compressive sensing and double random-phase encoding technique. Optik-International Journal for Light and Electron Optics, 124(16), 2514-2518. 

Ishtiaq Roufa, R. M., Mustafaa, H., Travis Taylora, S. O., Xua, W., Gruteserb, M., Trappeb, W., & Seskarb, I. (2010, August). Security and privacy vulnerabilities of in-car wireless networks: A tire pressure monitoring system case study. In 19th USENIX Security Symposium, Washington DC (pp. 11-13).   

Li, P., & Singh, H. (2010). U.S. Patent No. 7,817,558. Washington, DC: U.S. Patent and Trademark Office. 

Chang, D. C., & Chen, S. (2011). U.S. Patent Application No. 12/848,953. 

Cho, Y. S., Kim, J., Yang, W. Y., & Kang, C. G. (2010). MIMO-OFDM wireless communications with MATLAB. John Wiley & Sons. 

Elgala, H., Mesleh, R., & Haas, H. (2011). Indoor optical wireless communication: potential and state-of-the-art. IEEE Communications Magazine, 49(9).