ECEN 90 - Communications 2 Lecture Notes PDF

ECEN 90 - Communications 2 Lemuel G. Tatad College of Engineering and Information Technology Name  Learning Objectives After the completion of the chapter, students will be able to: 1. Co...

ECEN 90 - Communications 2 Lemuel G. Tatad College of Engineering and Information Technology Name  Learning Objectives After the completion of the chapter, students will be able to: 1. Connect the concepts of bandwidth, bit rate, bit error rate, power and complexity. College of Engineering and Information Technology  Introduction of Terms Bit rate is the rate at which data is processed or transferred. The unit of measuring bit rate in seconds. The bit rate measuring units range from bps for small units and Kbps, Mbps, and Gbps are from higher bit rates. Bit rate is also known as data rate. College of Engineering and Information Technology  Introduction of Terms Bit Rate table Source: GeeksforGeeks. (2024b, May 9). Bit rate. GeeksforGeeks. https://www.geeksforgeeks.org/bit-rate/ College of Engineering and Information Technology  Introduction of Terms Bandwidth is similar with the maximum bit rate in the communication network. It is the data transferring capacity of a communication channel or medium or it is the maximum rate at which bit's can be transferred from a source to a destination across the medium. The bandwidth indicated that how much time is required for transmitting or receiving the information over the provided network. College of Engineering and Information Technology  Introduction of Terms Bandwidth vs. Bitrate Table College of Engineering and Information Technology Source: GeeksforGeeks. (2024b, May 9). Bit rate. GeeksforGeeks. https://www.geeksforgeeks.org/bit-rate/  Introduction of Terms In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion or bit synchronization errors. The bit error rate or bit error ratio (BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval. BER is a unitless performance measure, often expressed as a percentage. College of Engineering and Information Technology  Introduction of Terms Example As an example, assume this transmitted bit sequence: 0 1 1 0 0 0 1 0 1 1, and the following received bit sequence: 0 0 1 0 1 0 1 0 0 1, The number of bit errors (the underlined bits) is in this case 3. The BER is 3 incorrect bits divided by 10 transferred bits, resulting in a BER of 0.3 or 30%. College of Engineering and Information Technology  Introduction of Terms Factors affecting the BER In a communication system, the receiver side BER may be affected by transmission channel noise, interference, distortion, bit synchronization problems, attenuation, wireless multipath fading, etc. The BER may be improved by choosing a strong signal strength (unless this causes cross-talk and more bit errors),by choosing a slow and robust modulation scheme or line coding scheme, and by applying channel coding schemes such as redundant forward error correction codes. College of Engineering and Information Technology  Introduction of Terms Factors affecting the BER Achieving a lower BER often comes at the cost of increased complexity, bandwidth utilization, or power consumption. Engineers and designers need to strike a balance between BER, system requirements, and available resources. Different applications have specific BER targets that need to be met to ensure reliable data transmission. College of Engineering and Information Technology  Introduction of Terms Improving BER Improving the Bit Error Rate (BER) in data transmission systems is a crucial goal for ensuring reliable and accurate communication. 1. Error Detection and Correction Codes: Implementing advanced error detection and correction codes, such as Reed-Solomon, Hamming, or Turbo codes, can significantly improve BER. 2. Modulation Schemes: The choice of modulation scheme can impact BER. More advanced modulation schemes, such as Quadrature Amplitude Modulation (QAM) or Phase Shift Keying (PSK), provide higher data throughput and better spectral efficiency. College of Engineering and Information Technology  Introduction of Terms Improving BER 3. Equalization Techniques: Equalization helps mitigate the effects of channel distortions and interference. 4. Signal Amplification and Filtering: Boosting the transmitted signal strength through amplification techniques helps overcome noise and interference, thereby improving BER. 5. Noise Reduction Techniques: Reducing noise levels at the receiver end is crucial for achieving a lower BER. 6. Channel Coding: Implementing channel coding techniques, such as Forward Error Correction (FEC), improves BER performance. College of Engineering and Information Technology  Introduction of Terms Improving BER 7. Transmit Power Control: Optimizing the transmit power according to the channel conditions can help improve BER. 8. Interference Avoidance and Management: Minimizing interference from other sources, such as adjacent channels or coexisting wireless devices, is crucial for achieving a lower BER. 9. Antenna Diversity: Utilizing multiple antennas at the transmitter and receiver can improve BER performance by mitigating fading and improving signal reception. College of Engineering and Information Technology  Introduction of Terms Improving BER 10. System Design and Optimization: A comprehensive system design approach that considers factors such as bandwidth, signal-to- noise ratio, modulation schemes, coding techniques, and channel characteristics is essential for achieving an improved BER. College of Engineering and Information Technology  Baseband Binary PAM Transmission System Model Overview of PAM Pulse Amplitude Modulation (PAM) is a method of transmitting digital data by varying the amplitude of discrete pulses. In a binary PAM system, two amplitudes represent binary digits (0 and 1). is the most efficient in terms of Figure 1. Waveform representation of PAM power and bandwidth utilization. College of Engineering and Information Technology  System Components Transmitter o Input Sequence: consists of binary digits (bits) is generated. o Pulse Generator: Converts the input bits into PAM signals. o Transmitting Filter: Shapes the PAM signals to minimize bandwidth and reduce interference. Channel o Channel: The medium through which the signal is transmitted, often affected by noise. The channel also adds noise to the signal at the receiver input. College of Engineering and Information Technology  System Components Receiver o Receiving filter: Removes noise from a signal to retrieve the original data. o Decision Device: Makes decisions based on the received signal to determine the transmitted bits. College of Engineering and Information Technology  System Components Figure 2. Baseband binary PAM transmission system College of Engineering and InformationSource: Technology Haykin, S. (2003). Communication systems, civilian. In Elsevier eBooks (pp. 409–432). https://doi.org/10.1016/b0-12-227410-5/00125-3  Intersymbol Interference (ISI) Intersymbol Interference (ISI) occurs when a pulse spreads out in such a way that it interferes with adjacent at the sample instant. Causes of ISI o Channel Distortion: Non-ideal channel characteristics can cause spreading of the signal. o Multipath propagation: a wireless signal from a transmitter reaches the receiver via many different paths. o Bandwidth Limitations: Bandwidth constraints in the communication channel can lead to distortion of the transmitted signal. College of Engineering and Information Technology  Intersymbol Interference (ISI) Figure 3. Examples of ISI on received pulses in a binary College of Engineering and communication system. Information Technology Source: Couch, L. W. (2013). Digital and analog communication systems. Prentice Hall.  Intersymbol Interference (ISI) Example: Assume polar NRZ line code. The channel outputs are shown below as “smeared” (width Tb becomes 2Tb) pulses (Spreading due to bandlimited channel). College of Engineering and Information Technology  Intersymbol Interference (ISI) Nyquist Criterion for Distortion less (Zero-ISI) Transmission. Nyquist proposed a condition for pulses p(t) to have zero–ISI when transmitted through a channel with sufficient bandwidth to allow the spectrum of all the transmitted signal to pass. The Nyquist Criterion can be expressed mathematically in two forms: one in the time domain and the other in the frequency domain. College of Engineering and Information Technology  Intersymbol Interference (ISI) Nyquist Criterion for Distortion less (Zero-ISI) Transmission. Time Domain Condition: The condition for the received pulse h(t) at discrete time intervals mTb (where Tb is the bit duration) is given by 1 𝑖𝑓 𝑚 = 0 h(mTb )ቊ 0 𝑖𝑓 𝑚 ≠ 0 It means that the overall received pulse must be zero at all multiples of the bit duration Tb, except at t = 0, which has the value of 1. College of Engineering and Information Technology  Intersymbol Interference (ISI) Nyquist Criterion for Distortion less (Zero-ISI) Transmission. Frequency Domain Condition: The frequency domain representation of the Nyquist Criterion states that the Fourier transform H(f) of the pulse must satisfy: 𝑘 1 σ∞ 𝑘= − ∞ 𝐻 𝑓+ = Tb, 𝑓 < 𝑇𝑏 2𝑇𝑏 This condition ensures that the frequency response of the pulse does not overlap with itself in the frequency domain, which corresponds to the time domain condition of zero overlap. College of Engineering and Information Technology  Intersymbol Interference (ISI) Nyquist Criterion for Distortion less (Zero-ISI) Transmission. However, the (sin x)/x type of overall pulse shape has two practical difficulties: 1. The overall amplitude transfer characteristic has to be flat over –B