Telecommunications Fundamentals and Network Standards

Digital Voice and PCM Data Rates

What is the data rate when voice is digitized through Pulse Code Modulation (PCM) in wired telephone networks? How is that number obtained?

The data rate is 64 Kbps. This is calculated based on a voice signal bandwidth of 4 kHz. According to the Nyquist sampling theorem, the number of samples required is 8,000 samples/sec. Using 8 bits per sample, the rate is determined as follows:

Rate = 8,000 samples/sec * 8 bits/sample = 64 Kbps.

Cellular Path Loss and 4G LTE-Advanced

[10 pts] Which one of the following numbers is a typical path-loss value in a cellular network, if a user is about 1 km away from the Base Station (BS): -1000 dB, -100 dB, -10 dB, 0 dB, 10 dB, 100 dB, 1000 dB?

The typical value is 100 dB.

[10 pts] What are the per-cell shared peak rates that the upcoming 4G LTE-Advanced wireless networks will provide in the downlink for stationary (no or limited movement) applications?

The peak rate is 1 Gbps.

Designing Next-Generation 20 Gbps Networks

(a) [15 pts] Suppose that you are involved in the design of a next-generation cellular network which targets to deliver a shared peak rate of 20 Gbps per base station in the downlink. Choose some appropriate values for the following:

• Bandwidth (BW): 315 MHz
• Spectral Efficiency: 8 bps/Hz
• Number of Antennas (for MIMO gain): 8

Calculation: Rate = 315 MHz * 8 bps/Hz * 8 antennas = 20.16 Gbps.

Benefits of Global Telecom Standards

[10 pts] State one reason why the telecom standards are beneficial for the vendors (such as Ericsson, Samsung, and Apple):

• Standards enable the vendor to sell products globally.

State one reason why the telecom standards are beneficial for the operators (such as Verizon, Bell Mobility, and AT&T):

• Standards enable operators to buy equipment from different vendors.
• They ensure interoperability between different systems.

Standardization Bodies: ITU, IEEE, and IETF

(e) [5 pts] The International Telecommunications Union (ITU) was founded in 1865. What application or service was being standardized at the time?

The service was the Telegraph.

(j) [10 pts] Give an example of a successful IEEE standard:

The 802 family (e.g., Ethernet and Wi-Fi).

(k) [5 pts] Give the acronym for the primary standards body for the Internet:

IETF (Internet Engineering Task Force).

ADSL and Switching Technology Comparison

(l) [10 pts] ADSL stands for "Asymmetric Digital Subscriber Line." What does asymmetric mean in this context?

It means that the transmission rates are different for the uplink and the downlink.

(m) [20 pts] State two advantages of packet switching over circuit switching:

• Bandwidth is consumed only when needed.
• It allows for speed conversion.

State two disadvantages of packet switching over circuit switching:

• Increased complexity.
• Variable delay (jitter).

Foundations of Information Theory and Noise

(n) [10 pts] Briefly explain the major contribution of Claude Shannon (without using equations):

Shannon provided the channel capacity theorem, which defines the maximum number of bits each symbol can carry at a given Signal-to-Noise Ratio (SNR).

(o) [10 pts] Who developed the noise model in digital communication systems?

The noise model was developed by Nyquist and Hartley.