Calculate the data rate required for robot to remote controller communication
Data rate = Number of bits sent per second
Total number of bits sent in two seconds=4+6+4+2
=16bits/2seconds
dividing by two 16/2
=8bps
b) Explain 3 types of suitable encoding techniques could be used to encode the
status string.
Since the robot sends data as a digital signal, it is imparative to use digital encoding schemes. The following digital encoding schemes could be used to encode the signals before placing it on the transmission media,(Makinen 2012)
This method is pretty straightforward. It is moreless what one would expect from encoding, We have one voltage level coerresponding to zero and another volatge level corresponding to ones, for example we can say a positive voltage level correspond to zero and a negative voltage level correspond to ones(Aldouri et al. 2011)
This is an example of differential encoding method. With this encoding method, it is not immediatelyt obvious which biot we are encoding simple by looking at the signal because each bit we encode will depend on the proceeding bit. We have to have some sort of a starting point. Assume we start at the lowest volatege level, but everytime we encounter a one, we will change the voltage level
It is not just the current voltage level that indicate which bit was being encoded, it is the whole history of the sequence that tell us what the current bit is.
Differential encoding scheme like this one can be useful in the presence of noise, because detecting a voltage transition is usually easier than assuring that voltage maintains a certain level (Chen et al. 2014)
This is essentially the opposite of bipolar AMI, pseudternary encodes ones with a flat line signal and encode zeros with altenating positive and negative volatages. Therefore we once again need to know what the preceding zero was encoded with to start off the signal. Let assumes before our sequence of bits start, we had a zero that was encoded with a negative voltage level, therefore
obstacle at 48 cm, all motors working (i.e. motor functionality 1111), and battery is 75%.
Status string=Accelerometer reading+Ultrasound obstacle detection reading+motor functionality status+battery level status
Step one: Convert all to binary
Acceleration=5m/s2 (Decimal notation)
Into binary=0101
Ultrasound=48cm (decimal notation)
Into binary=110000
Motor status=1111
battery level 0.75(decimal notation0
into binary =0.11
Combined status string will be concatenation of the individual status strings
=0101+110000+1111+0.11
=0101110000111111
Bit string = 01011100001111(digital input signal)
Carrier wave is of sinusoidal in nature as represented below
In ASK, we do not transmit any carrier signal when input bit is zero and when it is one, the carrier wave is transmitted as shown below(Teeka et al. 2011)
frequency of the sinusoidal carrier wave is varied(switched) depending on the digital input signal,then it is known as frequency shift keying. It is analogous to the FM modulation
bit string=010111000011111
carrier wave is shown below
To get the FSK, we change the frequency of the sinosidal carrier wave or it is switched according to the digital input signal as shown below
When one is to be transmitted , we have high frequency and when zero is to be transmitted we do not change the frequency of the carrier wave (Liu et al. 2011)
3.PSK(Phase shift keying)
In PSK, we vary the phase of the carrier signal based on the digital input signal, whenever there is a change in input signal e.g from 0 to 1 or from 1 to 0, a phase shift of 180 degrees takes place or 1 pie as shown below
11001101
Step 1
Data word=input bit sequences
=0101110001111
Additional digits =No of divisor digits-1
=8-1
=7
Step 2
Add the 7 digits to the data word to form the Augmented data word as shown below
Augmented data word=data word+additional digit
=0101110000111111+0000
=01011100001111110000
Step 3
Change the Augmented data word into polynomial
01011100001111110000
X18+X16+X15+X14+X9+X8+X7+X6+X5+X4
Step 4; Change the divisor into polynomial
11001101
X7+x6+x3+x2+1
Step 5;
Perform polynomial long division with divisor and the augmented polynomial as dividend, the quotient shall be the code word polynomial that shall be sent, the remainder shall be used for error correction
e) Briefly explain some other error control and flow control techniques that Sam
can use to ensure the accuracy of robot control
When data is transmitted, signal noise and synchronization errors can cause data to be lost or gambled up. So it i9s important to have a way of verifying that the data that is received is what was actually sent. The following ways can be used in the robot design to achieve this.
Sometimes, error detection alone is not enough when error are detected using CRC or checksum, then it necessitate re-transmission of damaged data. When data re-transmission is costly and transmission errors are common, then a more efficient scheme is EFC. In wireless applications like the robot system. FEC involves transmitting extra data so that certain errors can be corrected without any data being retransmitted. This method approach depends on a method called hamming distance. Hamming distance is a matrix for measuring the distance between two bit strings of the same length e.g consider the following bit strings
101101
110100
x x x
d(101101,110100)=3
FEC requires the creation of error correcting code. Specifically, both the sender and receiver will have a dictionary of code words, that looks like the following
00 00000
01 11100
10 10011
11 01111
There are many bit strings of length 5, that are not code words, this will allow the system to detect errors. Let’s encode the following sequence
01 00 01 11 11 10 00 10
the sender uses the dictionary to transfer each two bits sequence into a 5 bit code word
The resultant longer bit sequence will be transmitted. The length of the co9deword incurs a cost in the number of bits that need to bee sent. But by sending this bits, the system buys the need of re-transmission when errors occurs
At the receiver, the receiver has no knowledge where errors occurred, However, the receiver has also the same dictionary. It will try to decode each code word into its corresponding bit sequence. If the code word that it reads is in the dictionary, then it assumes the transfer went very smoothly. However when an invalid code word is received, it will compare it to the database of valid code words, to get an idea, which one it is most likely to have been, The algorithm does this using the Hamming distance. Having multiple bit errors is most unlikely than having few bit errors. Tyhe code word that is close to the dictionary code word in terms of Hamming distance will be picked and using the dictionary to decode.
If the distance between the invalid code word and the dictionary code words is tied by two in terms of hamming distance, a request for resend is sent to the original sender for re transmission. A case may arise when the undetectable errors is decoded by the receiver and make wrong assumption simple because the invalid code word matched one of the valid code word. It is recommended to use dictionary code words of longer bit strings to work around this scenario. Although it is still possible, it will have a low probability of occurring.
Flow control happens at the data link layer of the protocol stack. The notion behind flow control is that when two computers are communicating, you don’t want one to send data to the other so fast that it can not be processed. Data must be stored temporarily in a buffer in the receiver side, and if the sender sends data too quickly, then the receiver won’t be able to process the data and some data may be overwritten in the buffer before getting a chance to be processed. Flow control will prevent that. (Bergamasco et al. 2011)
Here the following types of frames are used,
Data; which represent the information to be sent
ACKnowledgement frame which is a a receipt for receiver have finished processing and needs the next frame in the sequence
The sender sends a data frame and it will only send the next item once it receives an acknowledgment of the previous data frame. In that way, the receive controls how fast the sender sends by sending back ACK. If the receiver is busy processing the data, it will not send an ACK, until it is ready and as a result, the sender won’t overflow the receiver
With stop and wait, one frames was allowed to be in transit at a time, which means we could only send one and wait for the ACK, which is very bad if the sender has to wait for a long time. This lowers the efficiency. With the sliding window flow control, it allow multiple frames not one, maybe two, three, seven to send before sender having to wait for ACK.
The transmitter can send frames 1, frames 2, frames 3 and eventually it will have to wait for ACK for frame 1, frame 2, frame 3 with the aim that while the ACK is coming back, the transmitter sends subsequent frames. To keep track of the frames, it is important to use sequence numbers to record which one has been sent and received. The sequence number must be fixed bit and it wraps around once the sequence is exhausted. This sequence number helps the sender to know what it has sent and the receiver use it to keep track of frames it has acknowledged.
Part II: Multiplexing and multiple access
Two single can be combine over a common pathway in perplexing. Multiplexing entails combining multiple user signals which are then transmitted over single common channel. This is related to multiple access which are applications that are used to allow various multiple users an opportunity to communicate with other users using one common channel. Multiple access is therefore an application of multiplexing technique. A WiFi hotspot can share its available connection to the Internet among many users using it simultaneously. This is achieved by providing them block of frequency which the mobile devices can use to transmit and receive data simultaneously. The throughput of the connection is directly proportional to the size of the given block. If you increase the block, you increase throughput since more devices can be accommodated in the bigger blocks. Since bandwidth is limited, most telecommunication systems have deployed several techniques aimed at making good use of this resource by sharing the same bandwidth among multiple users. The techniques includes, FDMA(Frequency Division Multiple Access), TDMA(Time Division Multiple Access), CDMA(Code Division Multiple Access).(Elgala, Mesleh, and Haas 2011)
FDMA uses FDMA to provides chunks of the frequency spectrum to its users for to use for data transmission. Generally, in FDMA the generated data is at basebannd and gets modulated at different frequencies. Guard bands used in FDMA are introduce with an aim of avoiding interference by the adjacent frequencies, AMPS are the first generation analog systems that used FDMA to provide each user a duplex channel with one way bandwidth of 40kHZ.
which uses TDMA to gives multiple users ability to share a one frequency band by allocating different slots of time to each device which wants to transmit. Given an N number of channels in TDMA, and that a single channel is allocated a time of time T units time, We can calculate the amount of time it takes for the internals to be rotated by taking N multiplied by T
2G systems such a gsm, GGPRSEDGE used this technique to ensure multiple access. Each device was allocated a time slot from the sets of slots in TDMA time slots with each given a bandwidth of 200Khz. With use of Dynamic allocation of resources improve the throughput of the channel since a good number of users could transmit, but a given channel only supported up to 8 active connections.
This is a unique way of achieving multiple access, where multiple users can access the base station over the same channel using the same frequency. Their is no dedicated channel between the transmitter and receiver. Different users are allocated different codes for multiple access by the base station.
The base station multiplies the signal from each user with its corresponding codes, then take the sum of the signal and transmit this common signal over the air. And each user can further correlates this received signal by the corresponding code of the user to extract its received symbol thereby multiple user s can simultaneously connect to the base station by using the codes (Ozluturk et al. 2011).
At the receiver, the receiver uses the same spreading code which is multiplied to the composite signal a process called de-spreading.
Lets take for example 2 users U0 and U1 , allocated codes Co[1,1,1,1] and C1[1,-1,-,1,1]
Each user has symbols A0 and A1 respectively
Multiply the symbol of each user with the respective code
A0*C0
=A0*[1,1,1,1]
=[A0,A0,A0,A0]
Similar, we multiply the symbol of A1 and C1
=A1*[1,-1,-1,1]
=[A1,-A1,-A1,A1]
The common signal is derived by summing the two signal of each user
A0*C0
+
A1*C11
[A0,A0,A0,A0]
+
[A1,-A1,-A1,A1]
=[A0+A1,A0-A1,A0-A1,A0+A1]
The common signal is transmitted over the same radio channel. From this signal, each user has to extract its corresponding symbol by correlating its code with the common signal that is multiplies its code with the common signal element by element and get the sum
C0=1111
A0=C0*Common signal
1 1 1 1 *
A0+A1 A0-A1 A0-A1 A0+A1
(A0+A1)+(A0-A1)+(A0-A1)+(A0+A1)
=4A0
The result is just a scaled version of A0
CDMA was used in 3G wireless systems such as HSPA+, CDMA, W-CDMA
OFDM is a new technology that takes a larger band and divides it into narrow sub bands. The bands operates different sub carriers and each data to be transmitted is placed in each separate sub bands and get transmitted at different carrier frequency. The sub bands narrowness is important in reducing ISI since the channel’s response time is rather flat compared to single carrier modes where the bands are so wide that equalization which is used to reduce ISI causes effective noise in the channel. OFDMA.
The above technique differs from the earlier multiplexing technique such as FDMA, TDMA, CDMA in the following ways,
In OFDMA, the carrier band is subdivided into narrow subsets called sub carriers, these sub carriers are the one used to transmit data from the transmitter to receiver. Unlike the earlier methods where a single channel was shared among multiple users.
For a signal to be used in OFDMA, it must meet the following special features,
scheme.
f(b)= channel bandwidth/allowable number of sub carriers
channel bandwidth=40MHz
allowable sub carriers=128 sub carriers
therefore f(b)=40MHz/128subcarriers
=0.3125MHz
=312.5KHz
T=1/f(b)
but f(b)=0.3125
T=1/0.3125
=0.0032 micro seconds
iii. Explain how OFDM overcomes the issue of inter symbol interference(ISI)
Signals in OFDMA are specially designed to avoid ISI by ensuring the signals achieve orthogonality with each other. This in effect allows the signals to occupy the same bandwidth without ISI, hence no need of guard bands. The different sub carriers can be packed closely to enhance channel efficiency
Part III: Wi-Fi
|
Room |
Number of Users |
Bandwidth per user |
Aggregate bandwidth |
|
Room 1 |
8 |
100mbps |
800mbps |
|
Room 2 |
8 |
100mbps |
800mbps |
|
Room 3 |
8 |
100mbps |
800mbps |
|
Room 4 |
8 |
100mbps |
800mbps |
|
Room 5 |
8 |
100mbps |
800mbps |
|
Lounge and Reception |
25 |
100mbps |
2500mbps |
|
Total |
65 |
6500mbps |
The BSS refer to the total coverage area of an access point that connects devices in a given locality.
Room 1
Area =L*W
=(10*10)m2
=100m2
BSS size for access point room 1=100m2
Room 2
Area =L*W
=(10*10)m2
=100m2
BSS size for access point room 2=100m2
Room 3
Area =L*W
=(10*10)m2
=100m2
BSS size for access point room 3=100m2
Room 4
Area =L*W
=(10*10)m2
=100m2
BSS size for access point room 4=100m2
Room 5
Area =L*W
=(10*10)m2
=100m2
BSS size for access point room 5=100m2
Room Lounge and Reception
Area =L*W
=(20*10)m2
=200m2
BSS size for access point room lounge and reception=200m2
ESS is a property of the 802.11 which relates with the property top combine two or more BSS to form a single sub-net under one ESS. BSS is a subset of ESS
ESS size=Total Coverage area of all the AP connected to the DS
=Area(Room1+Room2+Room3+Room4+Room5+Lounge)
=(100+100+100+100+100+100+200)m2
=700m2
Throughput is the actual data passing through the network per second
Each room throughput is (100*8)mbps
=800mbps
for five room =5*800
=4000mbps
The lounge has throughput of (25*100)
=2500mbps
Aggregated throughput=2500+4000
=6500mbps
your choice
IEEE 802.11ac is the recommended IEEE wifi substandard for the above setup.
This is the next generation WiFi standard. It gives up to three times faster connection speed compared to 802.11n. But it is not just about speed, WiFi networks this days need to connect more devices like smartphones, tablets and other wireless devices. The offices require on average 8 devices connected with all of them online.802.11ac was designed with mobile and multiple users in mind. 802.11ac is backward compatible, once you upgrade to 802.11ac, you will realize the benefits of smoother video stream, less buffering, faster surfing. Most laptops this days ships with 802.11ac standard hence it is important to use the standard(Gong, Nahm, and Kim 2008)
The following strategies can be applied to enhance the security of the network,
Change AP passwords
Protect the AP with a strong password. This is the gateway for the end devices hence should be protected. It is really common for people to leave the default password, but it is recommended to change it to a strong password
Only use WPA2 encryption
WEP and WPA are now considered weak encryption and should not be used. The best strategy will be to use the much stronger WPA2
Turn off WPS
WPS is a technology brought in for convenience the connection of new devices to the wireless network, a person could press a button on the AP and create a fast connection for a new device to join the network. From a hacking perceptive, this is the easiest way to join into the network by exploiting WPS
Look after the end devices
It is highly recommended to maintain antivirus software, local firewall, OS patches. This should apply to all the devices on the network including the mobile phones and smart TVs
Make SSID Obscure
SSID is the name of the network, it is recommended to hide the SSID by turning off the broadcast SSID feature. This provides a layer of protection. If for some reason the name must be used especially for the lounge and reception, then a random name that are not identifiable to the organization can be used
Consider MAC filtering
For more secure networks within the organization, MAC filtering can be used to ensure only the MAC addresses on the list shall be allowed to connect to the secure network. Those not on the list won’t connect even if they have a password. MAC filtering should not be used for lounge and reception since new devices join that network on daily basis (Liu and Chang 2009).
References
Aldouri, Muthana Y., S. A. Aljunid, R. Badlishah Ahmad, and Hilal A. Fadhil
2011 Bit Error Rate (BER) Performance of Return-to-Zero and Non-Return-to-Zero Data Signals Optical Code Division Multiple Access (OCDMA) System Based on AND Detection Scheme in Fiber-to-the-Home (FTTH) Networks. Optica Applicata 41(1): 173–181.
Bergamasco, Davide, Deepak Sharma, R. A. Rajesh, Silvano Gai, and Vibin P. Thomas
2011 Methods and Devices for the Coordination of Flow Control between a TCP/IP Network and Other Networks. Google Patents.
Bini, Dario, and Victor Y. Pan
2012 Polynomial and Matrix Computations: Fundamental Algorithms. Springer Science & Business Media.
Chen, Wen-Chuan, Ying-Min Chen, Chia-Ching Lin, Cheng-Xue Wu, and Jing-Yi Huang
2014 Asynchronous Master-Slave Serial Communication System, Data Transmission Method, and Control Module Using the Same Thereof. Google Patents.
Elgala, Hany, Raed Mesleh, and Harald Haas
2011 Indoor Optical Wireless Communication: Potential and State-of-the-Art. IEEE Communications Magazine 49(9).
Gong, Huazhi, Kitae Nahm, and JongWon Kim
2008 Distributed Fair Access Point Selection for Multi-Rate IEEE 802.11 WLANs. IEICE TRANSACTIONS on Information and Systems 91(4): 1193–1196.
Liu, Calvin Y., and Sheng-Chiao Chang
2009 Wireless Security Using Media Access Control Address Filtering with User Interface. Google Patents.
Liu, Xiang, S. Chandrasekhar, T. H. Wood, et al.
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.
Makinen, Jari M.
2012 Signal Encoding a Frame in a Communication System. Google Patents.
Ozluturk, Fatih M., Alexander Jacques, Gary R. Lomp, and John Kowalski
2011 Code Division Multiple Access (CDMA) Communication System. Google Patents.
Teeka, C., S. Songmuang, R. Jomtarak, et al.
2011 ASK?to?PSK Generation Based on Nonlinear Microring Resonators Coupled to One MZI Arm. In AIP Conference Proceedings Pp. 221–223. AIP.
Essay Writing Service Features
Our Experience
No matter how complex your assignment is, we can find the right professional for your specific task. Contact Essay is an essay writing company that hires only the smartest minds to help you with your projects. Our expertise allows us to provide students with high-quality academic writing, editing & proofreading services.
Free Features
Free revision policy
$10Free bibliography & reference
$8Free title page
$8Free formatting
$8How Our Essay Writing Service Works
First, you will need to complete an order form. It's not difficult but, in case there is anything you find not to be clear, you may always call us so that we can guide you through it. On the order form, you will need to include some basic information concerning your order: subject, topic, number of pages, etc. We also encourage our clients to upload any relevant information or sources that will help.
Complete the order form
Once we have all the information and instructions that we need, we select the most suitable writer for your assignment. While everything seems to be clear, the writer, who has complete knowledge of the subject, may need clarification from you. It is at that point that you would receive a call or email from us.
Writer’s assignment
As soon as the writer has finished, it will be delivered both to the website and to your email address so that you will not miss it. If your deadline is close at hand, we will place a call to you to make sure that you receive the paper on time.
Completing the order and download