Micro Robot Design And Related Concepts

Amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK)

Amplitude shift keying (ASK): digital data i can be defined as a  variation of amplitudes in the  a carrier wave . Two unlike amplitudes of transporter signal signify ‘0’ or ‘1’ (Sanghi). A unique pattern of binary digits that represent digital data are allocated to each of the finite number of amplitudes is used. Every bid encoded  equal number of amplitudes

Frequency shift keying (FSK): different digits are defined by a change in frequency, while the amplitude of the carrier remains the same . Two unlike occurrences approaching carrier frequency represent ‘0’ ,”1′.

Phase shift keying (PSK): This phase is changed to show data signals. The state of a bit is determined relative to that of the bit preceding it, in accordance with data being transmitted. (Sanghi).

1. i) The status string in binary

Acceleration  – 5m/s² = 0101

Ultrasound – 48cm = 0.48m = 0.01111

Motors – full = 1111

Battery – 75% = 10

e)Error and Flow Control

Error Control:

Hamming Code

It is a method that utilizes redundant bits which are included with the original data. The bits are ordered in a manner to allow for detection of a corrupt bit since unlike indecent bits yield different fault results. Once identified, the receiver reverses its value and corrects the error.

A Simplex Stop-and-Wait Protocol

The Sender sends data and waits for the response from Receiver.

If the Channel has errors there will be no acknowledgement from the receiver because it did not receive the correct data.  This will disable the sender from sending the next data hence the communication will end.

Sliding Window Protocol

Here, both communicating parties use buffer of the same size, eliminating the necessity to wait for the sender to transmit the next data, it just sends one after the other without having to wait of the receiver’s acknowledgment.

Part II: Multiplexing and multiple access

TDM

In Time-division multiplexing, multiple data streams with different frequencies are transmitted on the single link by separating the signal into many segments, so that each signal materializes on the line for  little time as possible in an alternating manner. Single data are collected together at equally time streams. Therefore, these signals being transmitted appear as if they are moving concurrently as sub-channels in one message channel, but in reality they are taking a different path.

• At the transmitter, several signals are transmitted simultaneously over a time sharing basis. Each signal utilizes all the frequencies in its allocated time slot, for the duration of the transmission.
• At the receiver, the sampler has to be synchronized with the incoming waveform to reassemble the data streams.

There are two types of TDM:

1. Synchronous TDM (STDM)

 STDM uses the following procedure:

1. All devices are given chances to transmit data on the data link.
2. Individually device are given equally time to transfer or move data on the link that is available. The total speed of various input lines does not exceed the capacity of path. The speed of the input links do not exceed the path or data link.
3. Individually device positions its information on the part when its time reaches; taking turns in a fixed order and fixed time (interleaving).
4. Interleaving is done byte by byte.
5. The time slot remains empty for devices that do not have data to transmit.
6. Each frame has a number of time slots that is equivalent to the number of transmitting devices.

Asynchronous TDM  

1. Here the slots are only given to devices that have data to be send
2. Incoming data lines are scanned and the device  receives  data and send to the destinations that required
3. If the data available is not enough to fill the available slots then the same slots are filled with data partially.

In the above illustration shows  how  data  flows :

FDM

This method allow numerous data signals to be joint for concurrently transmission through a shared link. A data link is always used for each frequency transmission via a communication link. This allows frequencies to be shifted through   spectrums so that it can be transmitted in high speed .Has a oscillator generator  that generates the frequency  and transmits it to the required end. The diagram show the multiplexer

CDMA

This is a channel get to strategy where a few transmitters can send data at the same time finished a solitary correspondence channel. This enables a few clients to share a data transfer capacity. It utilizes spread range innovation and an extraordinary coding plan

1. CDMA employs a combination of analog-to-digital conversion with spread spectrum technology.
2. After digitizing the data, it is spread out over the whole available bandwidth.
3. The frequency of the transmitted signal is varied according to a defined code so it can be captured only by a receiver whose frequency response is programmed with the same code.
4. Multiple users can access the same channel simultaneously because of the use of independent spreading codes and synchronous reception.
5. Data is spread by use of a code independently of the data in order to achieve an increased bandwidth.
6. To receive the data, the receiver must have knowledge of the spreading code, which is used to decipher the transmitted data (radio-electronics.com).
7. b) OFDM

Features of OFDM

• Source data is processed to rectify coding for correcting errors, interleave and map bits onto symbols.
• Adding a recurring prefix to the frame to be sent helps maintain Orthogonality during channel transmission.
• The cyclic prefix can be a means of detecting the start of each frame.
• Demodulation of the signals is done using FFT.
• Channel equalization is estimated using a training sequence or pilot symbols at allocated sub-carriers.

1. For 48 subscribers what should be the subcarrier bandwidth ( fb ) ?

According to a Rohde and Schwarz whitepaper on 802.11 ac, the subcarrier bandwidths will be as follows:

For a 40MHz transmission, maximum number of subscribers will be 128 transmitting signals from -58 to -2 and 2 to 58MHz.

1. Suitable subcarrier bit time for orthogonality orthogonality requires that the sub-carrier spacing is:

Where T_u seconds is symbol duration and k is a positive integer, equal to 1.

Therefore, with 48 sub-carriers, the total passband bandwidth will be

B ≈ 48·Δf (Hz).

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

The fading distortion in the channel causes ISI in a OFDM demodulator and compensating for it introduces the problem of noise enhancement. Frequency domain equalization process inserts frequency domain pilot symbols in each frame.

Time Domain Windowing

Windowing a signal to be transmitted by multiplying with a suitable function works to diminish the interference by causing the spectrum of the signal wave form to be more concentrated, then same window is used receiver-side to reconstruct the original signal. The window functions need to satisfy the Nyquists vestigial symmetry criterion for ISI to be eliminated.

Pulse Shaping

A frequency offset causes loss of orthogonality due to the spectral null not coinciding to the peak of the individual carriers and as it increases the ISI power increases too. Pulse shaping reduces the side lobes in order to maintain orthogonality.

PART III

1. Design the network specifying the locations of access points and distributions system showing the backbone network.

BSS size is the range of an AP, in this case,

Radius r =10m.

BSS = π*r² = 3.142 * 10 = 31.42m²

ESS size is the size of the channel extended over multiple Access Points.

In this network, we have 8 Access Points each with BSS of 31.42m².

31.42m² * 8 = 251.36m²

1. Throughput

Where RWIN is the TCP Receive Window and RTT is the round-trip time for the path.

Therefore:

100/0.02 = 5000bits/s = 4.882Mbps

1. Suitable IEE standards

5.15 GHz to 5.825 GHz (U.S)

-5.15 GHz to 5.725 GHz (Europe)

1. Securing the network

Enable logging

Switch on logging of devices and network activity

Login credentials

Change login credentials from the factory default to a new username and a complex password made up of letters, numbers and symbols

Firmware update

Regularly check for, and install firmware updates for the routers, as well as software an driver updates for the workstations.

Encryption

Enable Access Point Encryption such as WPA or WPA2 to protect data sent over that network

Physical security

Aps devices should be kept in locked cabinets to avoid being interfered with.

Secure the 802.1X client settings

This prevents attacks on the server.

References:

Cheng, H., & Li, X. (2010). Partial encryption of compressed images and videos. IEEE Transactions on signal processing, 48(8), 2439-2451.

Nosratinia, A., Hunter, T. E., & Hedayat, A. (2004). Cooperative communication in wireless

 networks. IEEE communications Magazine, 42(10), 74-80.

Lueng, K. T., Dao, S., & Shek, E. (2009). U.S. Patent No. 7,483,693. Washington, DC: U.S. Patent and Trademark Office.

Lee, H. Y., Chang, R. C., Huang, L. Y., & Chiang, M. L. (2010). U.S. Patent No. 6,657,981.

Washington, DC: U.S. Patent and Trademark Office.