Apr 5, 2022

Small cells – Understanding Network and Security for Far-Edge Computing

So far, we have been discussing macrocells. They are large arrays of antennas that are typically mounted on their own tower and meant to service all of a CSP’s customers for a radius measured in kilometers. The ever-growing demand for new mobile devices has driven a market in small cells. These are small, lower-powered access nodes that are deployed for specific uses.

CSPs add small cells to their existing networks to increase coverage in rural areas, to service more devices in an area of particularly dense usage, or to provide service indoors. Small cells are also found in most private 5G networks. Small cells are broken up into femtocells, picocells, and microcells – each of which has a different range and supports a different number of users.

5G frequency spectra

Unlike 4G/LTE, 5G frequencies are split into three range groupings, each in a different region of the spectrum:

Figure 3.27 – 5G frequency band utilization

Cellular Vehicle-to-Everything (C-V2X)

Vehicle-to-Everything (V2X) is a set of specifications that encompass multiple types of wireless communication between a vehicle and its surroundings. This includes other vehicles, infrastructure, networks, and even pedestrians. V2X communication has the potential to revolutionize transportation, making it safer, more efficient, and more sustainable. C-V2X, however, is based on 5G (although it can use 4G/LTE in a more limited fashion).

V2X can be broadly categorized into four subtypes:

Vehicle-to-Vehicle (V2V): This communication occurs between vehicles on the road, allowing them to exchange information about their position, speed, and direction. This enables advanced Driver-Assistance Systems (ADASs) to prevent collisions, optimize navigation, and facilitate cooperative driving.

Vehicle-to-Infrastructure (V2I): In this type of communication, vehicles interact with roadside infrastructure such as traffic signals, road signs, and smart city sensors. This allows for real-time traffic management, improved safety measures, and enhanced navigation guidance. China is leading the way in this area. Nearly 90 cities have already partnered with local wireless network operators, deploying tens of thousands of roadside units to demonstrate intelligent highways and urban intelligent networked roads.

Vehicle-to-Pedestrian (V2P): This type of communication occurs between vehicles and pedestrians or cyclists, using devices such as smartphones or wearable technology. V2P communication can help prevent accidents by providing alerts to both pedestrians and vehicle drivers about potential collisions.

Vehicle-to-Network (V2N): This type of communication connects vehicles to various networks, including the internet, cellular networks, and cloud-based services. V2N communication can provide vehicles with updates on traffic, weather conditions, and other relevant information to enhance their performance and safety.

Of note is that, unlike most other 5G technologies, C-V2X does not necessarily require an MNO’s infrastructure to function. It can operate without a SIM, without network assistance, and uses GNSS as its primary time synchronization source. Today, about 50-60% of vehicles in North America are equipped with a cellular modem. The decision-making process within the automotive industry on whether to standardize on DSRC/802.11p or 5G for V2X has been long and drawn out but has finally settled on using cellular as the standard going forward.

According to the 5G Automotive Association (5GAA), auto manufacturers that are currently producing C-V2X capable models include Audi, BMW, Daimler, Ford, Lexus, Nissan, and Tesla.

Aug 18, 2021

ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING (OFDM) – Understanding Network and Security for Far-Edge Computing

This is a scheme in which multiple closely spaced orthogonal subcarrier signals with overlapping spectra are transmitted to carry data in parallel.

In traditional Frequency Division Multiplexing (FDM), the subcarriers (also known as channels) are kept apart using a little bit of space between them called a guard band:

Figure 3.18 – FDM using guard bands

This is done to prevent crosstalk, noise, or interference between the channels. It also makes it easier for the demodulators to single out the channels when demuxing them.

OFDM deliberately overlaps the channels in a specific way – this is where the orthogonal part comes in. Orthogonal means “at right angles,” but in this context, it refers to a precise mathematical relationship between how the channels are spaced across the frequency band. This technique can save as much as 50% of the bandwidth, which can now be used to carry additional channels:

Figure 3.19 – OFDM

OFDM uses digital signal processing techniques to perform coherent demodulation on these overlapping channels 7. The mathematics are beyond the scope of this book. At its core, this is simply another example of how we can exploit the fact that light always travels at the same speed. OFDM techniques can, and often are, used in combination with MIMO.

7 Fourier transforms can be performed to convert the time domain of a digital signal’s square waves into frequency domains corresponding to the channels.

Shannon-Hartley theorem (signal-to-noise ratio)

Developed in the 1940s, the Shannon-Hartley theorem describes the maximum rate at which information can be transmitted over a communications channel of a specified bandwidth in the presence of noise:

Here, we have the following:

C is the channel capacity in bits per second

B is the bandwidth of the channel in hertz

S is the average received signal power in watts

N is the average power of noise/interference in watts

Let’s zero in on the two most important terms to remember:

Signal (S): Average power of the received signal in watts

Noise (N): Average power of noise (that is, interference) in watts

These two terms are grouped into a single expression known as the Signal-to-Noise Ratio (SNR). An SNR of 2:1 means there is twice as much signal as there is noise. An SNR of 1:1 means there is the same amount of noise as there is a signal.

Another way to put this is to say a signal that is suffering throughput loss from degradation due to interference can be improved by increasing the signal’s power 8.

8 Keep in mind that increasing the power of your signal can create interference for others. This is why there are often laws limiting how powerful a given device’s transmitter is allowed to be.