Which of the following is a reason radio is considered as an active medium?

11.4.2 Challenges Introduced by Advanced Antenna System

In 3GPP RAN4 it is assumed that an AAS base station comprises a system in which active radio/transceivers and antenna components are integrated, which is capable of dynamically varying the radiation pattern in a controlled manner. The ability to dynamically adjust the radiation pattern contrasts with the systems described in Section 11.4.1, in which the radiation pattern is fixed. AAS base stations may be built around a number of different architecture concepts, ranging from fully digital, in which each individual antenna element is driven by an individual radio transmitter to hybrid, in which groups of elements (e.g., columns) are driven by a transmitter. Chapter 14, considers in more detail the application scenarios and benefits/drawbacks of each architecture option.

A first and very significant challenge for an AAS is that when there is a large number of radio transmitters and receivers, the feasibility of building antenna connectors for each individual radio transmitter together with a testing setup that enables testing of the combined response of individual radios is severely compromised. For large arrays and in particular for millimetric-wave systems, provision of test connectors becomes unfeasible. Even for systems for which connectors can be provided, since beamforming is a key component of the base station function it is desirable to set some requirements that encompass the antenna array as well as the radio/transceiver. Thus, for AAS base stations, it is necessary to specify requirements and corresponding relevant metrics and perform conformance testing (as well as other forms of testing such as research and development testing and manufacturing testing) over the air, that is, by means of analyzing signals radiated from the base station and/or exposing the base station to radiated signals in a controlled environment. OTA testing of base stations is a major paradigm shift for base station testing that has resulted in significant work in standardization and regulatory fora. However, OTA testing alone is not the only challenge to consider in setting regulatory requirements for AAS base stations.

The beamforming functionality of the base station is in general distributed between so-called analog beamforming, which takes place within the antenna element groups driven by each individual transmitter or receiver and digital beamforming, which takes place in the digital domain prior to conversion to analog transmission (as described in Section 7.3). The radiated beam pattern is the composite result of all digital and analog beam steering, antenna and subarray radiation patterns, and transceiver properties. For any conformance requirements that need to consider the radiation pattern of the base station, the requirements need to be placed on the AAS BS as a whole such that the impacts of all beamforming mechanisms in addition to transceiver performance are captured.

The radiation pattern of unwanted emissions from an AAS base station depends on several factors. Some unwanted emissions components are generated by random noise-like processes, which are uncorrelated between different transmitters. These components will not experience coherent beamforming and will be radiated according to the pattern of the element groups driven by each transmitter. Other components are related to distortions of the wanted signal, such as intermodulations. If the wanted signal contains a number of beams, and/or considering that the phase impact of intermodulations will vary in a frequency-specific manner, the pattern of emissions arising from such transmitter distortions is likely to be beamformed, but potentially with a different pattern to that of the wanted signal (See Fig. 11.9). A further category of unwanted emissions arises from specific components of the transmitter, for example, local oscillators (LOs) that give rise to narrowband interference. These components may also experience coherent beamforming gain through the array, and the beam pattern may or may not be aligned with the wanted signal depending on the array and transmitter architecture.

Fig. 11.10 depicts a simulation result illustrating the direction of unwanted emissions components in relation to two carriers. In the center, the spectra and angular distribution of the two carriers are observed. The carriers have different beam directions. To the left and right, the spectra and angular distribution of the intermodulation products are visible. The IM has peaks of radiation, but they are not aligned with the peaks of either of the carriers.

The fact that both the wanted signal and the unwanted emissions are subject to time-varying beamforming implies that evaluation of interference and co-existence properties cannot assume a fixed antenna pattern as is the case for non-AAS systems. Consideration must be given to both the potentially wide variation in beam patterns of different implementations and to the implications of time-varying beam patterns on aspects regulated by conformance requirements such as co-existence with other systems. Section 11.5.2 outlines the approach and conclusions for setting emissions and power requirements for AAS base stations. Furthermore, the spatial pattern of the wanted signal and interference or distortion may differ for the reasons outlined above. For this reason, requirements based on quantities that are ratios of power levels, such as ACLR and EVM, will vary in space and will for many directions not be the same as the ratios achieved at the transmitting radios. Additional consideration is needed on the implications of the spatial variation of relative requirements.

In the receiver direction, a discrepancy between the portion of the antenna aperture related to each individual receiver and that of the whole array considering all types of beamforming necessitates careful evaluation. The sensitivity of the array as a whole depends on the combined beamforming within the array, the NF of the radio receivers, and the baseband implementation. Some of the receiver requirements are, however, designed to set limits on desensitization (degradation of sensitivity) caused by the introduction of interferers. For example, the receiver blocking requirement introduces a high-power interferer and regulates the power level at which receivers saturate and any other forms of desensitization that may arise. The blocking interferer causes distortions in individual radio receivers; in the worst-case overloading of the receiver ADCs that causes the receivers to cease to operate. The distortions may be nonlinear and uncorrelated between different receivers. A key problem when considering such effects and the associated radio requirements is that the impact of the interferer on individual receivers depends on the gain of subportions of the array aperture (i.e., subarray radiation patterns), whilst the sensitivity itself depends on the whole array architecture and radiation pattern. The implication of this discrepancy between which part of the aperture is relevant for which type of signal can differ depending on the receiver architecture, which is problematic when attempting to create a generic radio requirement that treats the base station as a black box (Fig. 11.11).

Section 11.4.1 mentioned that non-AAS radio requirements defined unwanted emissions on each individual radio. For an AAS base station, setting unwanted emissions requirements per individual radio becomes problematic for a number of reasons. Firstly, it is desirable to set requirements on the base station as a whole that do not depend on the individual AAS base station architecture, and it would be undesirable for different array architectures with different numbers of transmitters to present differing levels of interference to the outside world. Secondly, it would be unacceptable for an AAS BS with a large number of transmitters to present an unacceptably large level of total interference simply due to an emissions requirement being applied to each transmitter individually.

Apart from the radio requirements, the baseband demodulation requirements are potentially challenging for an AAS BS. The baseband demodulation requirements typically include a stimulus signal that is modulated based on a model of a multi-path fading environment. Without access to antenna connectors, it is highly challenging to create a controlled and reproducible multi-path fading environment in an OTA test.

In summary, the architecture and functionality of AAS base stations gave rise to several challenges for setting conformance and regulatory requirements. The need for OTA testing is a paradigm shift without precedent from previous base station technologies. The complexity in emulating real multi-path fading environments in an OTA test chamber is prohibitive and thus current state-of-the-art OTA testing without multi-path was considered. Apart from the new approach to testing, other aspects to consider included the impacts of beamforming, time-varying unwanted emissions, various types of architectures with different spatial behaviour and different responses to stimulus signals. Furthermore, the need to set requirements on the whole base station system (comprising antennas, radios, and digital processing) that do not depend on the architecture necessitated careful evaluation.

11.1.1 Communication Device

The communication device gives the smart object its communication capabilities. For wireless smart objects, the communication device typically is a radio transceiver. The word transceiver is a portmanteau of the two words transmitted and receiver. As the name indicates, a radio transceiver is able to function both as a transmitter and receiver of radio messages. For a wired smart object, the communication device connects to a wired network connection such as Ethernet or Powerline communication (PLC). In this section, the focus is on radio transceivers, and the discussion of wired PLC connections can be found in Chapter 12.

Different types of radio transceivers have different amounts of built-in processing capabilities. The simplest radio transceivers only send and receive individual bits of information into the air, whereas more capable transceivers package the information into packets, form headers, and even encrypt and decrypt the data using secure encryption methods.

Of the hardware components of a smart object, the radio is usually the most power-consuming component. Compared to the power consumption of the microcontroller or the sensors, the radio transceiver often uses ten times as much power. This is due to the processing required for modulating and demodulating the radio signal. For low-power radios, only a small portion of the power consumption is used to send the radio signal into the air. The conclusion is that listening is as power consuming as sending.

Because the radio is the most power-consuming component, and because idle listening is as expensive as sending data, the radio must be switched off to conserve power. When the radio is switched off, however, it is not able to receive any data. To create multi-hop networks, the radios of all devices in the network must somehow be synchronized so they are able to receive data while conserving power. in Section 11.3, we look into a number of duty cycling mechanisms that keep the radio off for most of the time, while still allowing data to be exchanged between the nodes.

Figure 11.3 is an example of a Radiocrafts single-chip radio transceiver for smart objects. The Radiocrafts chip contains both a radio transceiver and a microcontroller. The radio transceiver, manufactured by Texas Instruments and called CC2430, is compatible with the IEEE 802.15.4 radio standard and capable of transmitting and receiving individual packets, rather than individual bits. The bit rate of the radio transceiver is 250 Kbits/s.

10.6 Scheduling

Sensor nodes share the wireless medium. Therefore, they need a Medium Access Control (MAC) protocol to coordinate access. We discussed the IEEE 802.11 protocol in detail in Chapter 7. However, in a sensor network, energy efficient MACs are extremely important, and this forces us to look at MAC protocols closely.

Even when a sensor node is not transmitting but merely listening to the medium, significant energy is spent. This is because the electronic circuitry in the radio transceiver has to be kept on. Studies have shown that the ratio of energy spent in transmitting a packet to a receiver at unit distance, to that spent in receiving a packet and to that spent in listening for the same length of time, is 3:1.05:1. (Of course, when the receiver is far away, a transmitter would use more power and therefore, the energy spent would be more). The notable point here is that a sensor spends the same order of energy in simply listening on the medium as in actually receiving a packet.

Since saving energy is so important, we need to understand how energy can be wasted. The following causes can be discerned.

Idle listening: If the medium is idle and yet a sensor node's radio transceiver is on, then it is spending energy unnecessarily.

Collision: If transmissions collide, then all packets involved are garbled, leading to waste of energy all around.

Overhearing: Overhearing occurs when a node receives a packet that is not addressed to it.

Control packet overhead: From an application's point of view, energy spent in carrying information bits is energy usefully spent. It is desirable that the energy spent on control path activities, like channel reservation, acknowledgement, and route discovery, be as small as possible.

A good sensor MAC protocol leads to savings on all four of these fronts.

Sensor MAC protocols are significantly different from other wireless MAC protocols (like IEEE 802.11) because they can put the sensors into the sleep state. In this state, the radio transceiver is turned off completely. Nodes wake up periodically, listen on the medium for a short while, and then go back to sleep. This reduces idle listening drastically, and is a major reason for energy savings.

However, it is also immediate that as a result of the cycling between sleep and wake states, the latency in transferring information across nodes can be considerably increased. A transmitter has to hold on to the information it must send until it is certain that the receiver is ready and listening. Nevertheless, in many application scenarios, the increase in latency does not cause difficulties. For example, in an intrusion detection application, the speed at which the network transfers information is orders of magnitude higher than that of an intruder's movements, even when additional latency due to sleep-wake duty cycling is considered.

10.6.2 IEEE 802.15.4 (Zigbee)

The other sensor MAC protocol that has received wide attention is the IEEE 802.15.4 MAC. The protocol was introduced first in the context of Low-Rate Wireless Personal Area Networks (LR-WPANs). The PHY and MAC layers in LR-WPANs are defined by the IEEE 802.15.4 group, whereas the higher layers are defined by the Zigbee alliance.

IEEE 802.15.4 defines two types of devices: a Full Function Device (FFD) and a Reduced Function Device (RFD). The FFDs are capable of playing the role of a network coordinator, but RFDs are not. FFDs can talk to any other device, while RFDs can only talk to an FFD. Thus, one mode of operation of the IEEE 802.15.4 MAC is based on a hierarchy of nodes, with one FFD and several RFDs connected in a star topology (see Figure 10.12). The FFD at the hub, which is a network coordinator, plays the role of a cluster-head, and all communication is controlled by it. In the peer-to-peer topology, however, all nodes are equally capable; all are FFDs.

Figure 10.12. IEEE 802.15.4 nodes in a star topology.

Figure 10.13 shows the superframe structure defined for IEEE 802.15.4. The superframe begins with a beacon. Nodes hearing the beacon can set their local clocks appropriately, so that they go to sleep and wake up at the same time. This means synchronized operation.

Figure 10.13. The Zigbee MAC superframe structure. CAP and CFP stand for Contention Access Period and Contention Free Period, respectively. GTS means Guaranteed Time Slot. The other parameters in the figure are defined in [61].

The superframe is divided into an active and an inactive period. During the inactive period, nodes sleep. The active period consists of at most three parts—beacon transmission interval, the Contention Access Period (CAP) and an optional Contention Free Period (CFP). During the CAP, nodes contend using slotted CSMA/CA, as in IEEE 802.11 (see Chapter 7). In the CFP, a node can be allotted Guaranteed Time Slots (GTSs) by the network coordinator. Nodes request for GTS allocation by sending explicit GTS allocation requests. Transmitted frames are always followed by Inter-Frame Spacings.

20.3.3 Zigbee and the PIC microcontroller

Zigbee is an interesting standard to engage with, and a natural one to apply with PIC microcontrollers. A possible physical implementation of a Zigbee node is illustrated in Figure 20.3.

The link is through a single-chip radio transceiver, such as the Chipcon (now acquired by Texas Instruments) CC2420 [Ref. 20.8]. A microcontroller interfaces to this through an SPI link and certain control lines. Microchip has produced extensive firmware which can be adapted to apply the protocol. An example, described in Ref. 20.9, allows a Zigbee Coordinator or RFD to be implemented. Figure 20.4 shows a Derbot implementation of the Zigbee protocol, making use of a Microchip demo card.

18.3.2 LoRaSim and extended LoRaSim

LoRaSim [28], a LoRa network simulator, is a discrete-event simulator developed using the Python programming language’s SimPy package. The simulator implements a radio propagation model based on the well-known log-distance path loss model. The sensitivity of a radio transceiver at room temperature with respect to different LoRa spreading factors and BWs settings can be calculated. It is useful for simulating collisions in LoRa networks and to analyze scalability. LoRaSim allows to simulate LoRaWAN networks with a single application. Practical deployments of multiple IoT applications such as utility meters, intelligent transport, parking systems, and many such applications are deployed on a single LoRaWAN network. Extended LoRaSim [29] allows simulating a LoRaWAN running multiple applications. LoRaWANSim is a simulator which extends the LoRaSim tool to add support for the LoRaWAN MAC protocol, which employs bidirectional communication. This is a prominent feature not available in any other LoRa simulator. Consequently, it is suitable to predict the performance of LoRaWAN-based networks such as achievable network capacity and energy consumption versus reliability trade-offs associated with the choice of number of retransmission attempts through extensive simulations.

LoRaWAN packet generator [30] is a command-line tool for generation of user datagram protocol (UDP) packets that can be sent from the PC host to the LoRa network server. It simulates LoRaWAN gateway and sends the UDP packages defined by the “Gateway to Server Interface Protocol” defined in Semtech document ANNWS.01.2.1.W.SYS [31]. Basically, it acts as a LoRa node and a gateway and useful to test the LoRa network server deployments and integrations in the absence of expensive network hardware setup.

26.1 GE CommerceGuard

The GE CommerceGuard system provides global tracking of containers as well as immediate notification if the security of the container is breached. The system is semi-IP-based where the end devices are not IP end points, but communicate with fixed readers that are IP end points. The CommerceGuard system was developed in 2002 by the company AllSet Marine Security AB and sold to General Electric in 2005. Its container security device and attachment to an intermodal container are shown in Figure 26.1.

The CommerceGuard system consists of two components: container security devices and readers. The container security devices are placed on the containers and communicate with the readers. Readers are placed both at ports and reloading locations as well as on the ships. There are also mobile readers that are attached to mobile phones or laptops.

The readers communicate with the container security device using a low-power radio and a proprietary protocol. The readers are connected to the Internet and communicate using TCP/IP over an Inmarsat satellite connection. The readers have contact with a database that maintains the location of all container security devices in the system. Customers and users can interact with the system through the database. The CommerceGuard architecture is shown in Figure 26.2.

The container security device consists of a microprocessor, a radio transceiver, a power source in the form of a battery, and a set of sensors. Different container security devices have different configurations of the sensors, but all container security devices have a sensor that detects the opening and closing of the door. The door sensor can also detect if someone is trying to open the door, but fails.

Container security devices can be equipped with additional sensors such as temperature, humidity, vibration, radioactivity, and motion. A particular set of sensors is configured depending on the goods transported in the container. The sensors collect data for storage and act on the data according to a set of application-specific rules.

The radio transceiver on the container security device is duty cycled to provide a long lifetime when running on batteries. The reader and security device communicate using an out-of-band protocol to establish a duty cycle that fits the activities of the location at which the reader is deployed. Readers on a ship, where containers are likely to be present for a longer time and where there is no container mobility, announce a duty cycle that allows the security devices to keep the radio off most of the time. In contrast, readers placed at a busy sea port with high container mobility announce a high duty cycle. Thus security devices keep their radio on for longer amounts of time, allowing for more frequent communication with readers. This allows the readers to communicate with security devices as they are moved between ships and freighter trucks while maintaining low-power consumption for the security devices.

Readers are either stand-alone fixed readers as shown in Figure 26.3 or implemented as an add-on to a phone. The purpose of the reader is to communicate with the container security device using the short-range radio. The readers run the uIP IP stack [64]. The IP stack enables IP-based communication with the device. This reduces the need for custom communication software, leading to lower deployment costs.

Users and customers interact with the CommerceGuard system using a web browser, as shown in Figure 26.4. The user interacts with the database that contains information about the security device’s location and physical conditions inside the containers to which they are attached.

3.1.2 Topology modeling

In Figure 5.4 we show two possible topologies that can be figured out for CR-based WSNs. How to model the deployment in this type of network is perhaps more important than in “traditional” CRNs, since CWSNs are prone to change more frequently than CRNs. Just to provide an example, the main difference between the hardware structure of a classical sensor and a CR Sensor Node (CRSN) is represented by the cognitive radio transceiver. Indeed, a CRSN is able to dynamically adapt the communication parameters, such as carrier frequency, transmission power, and modulation.

In [23], Akan et al. propose four different types of topologies, namely (i) Ad Hoc CWSNs, (ii) Clustered CWSNs, (iii) Heterogeneous and Hierarchical CWSNs, and (iv) Mobile CWSNs. They outline that, despite the increased challenges and complexity, the last two types of topologies, due to the heterogeneity and the mobility aspects, can be very effective and beneficial for increasing the potentiality of the network. In fact, either the presence of more powerful devices, or the possibility of moving some devices towards a specific and useful position, can be exploited to increase the lifetime of the whole network, by decreasing the energy consumption.

Figure 5.4(a) describes a clustered CWSN topology, where there is a common channel to exchange various control data, such as spectrum sensing results, spectrum allocation data, neighbor discovery, and maintenance information. This type of topology is an appropriate choice for effective dynamic spectrum management, with a local common control channel approach. On the other hand, Figure 5.4(b) depicts the architecture for heterogeneous and hierarchical CWSN, which incorporates special nodes (i.e., actor nodes) equipped with renewable power sources, and acting in additional tasks like local spectrum bargaining.

2.2.1 Miniature energy-harvesting wireless sensor node

Wireless sensor network is an emerging technology to enable distributed sensing function inside buildings. Today, the concepts of smart meter and smart appliance rely on a wireless sensor network. Hereafter, we review and discuss the hardware of a wireless sensor network.

As shown in Fig. 4, a wireless sensor node is usually composed of several parts: an antenna, a radio transceiver (e.g., CC2500 chip), and microcontroller circuit (e.g., MSP430F2274), and an energy supply source (e.g., battery pack). The wireless sensor network was initially reported to monitor living habits of outdoor animals. Later, researchers presented to install wireless sensor networks inside buildings for building operation management. Through a comprehensive interview with building operation staff and managers, ten key design challenges have been identified and shown in Table 1 [7]. Power consumption (battery lifetime) and data communication of a wireless sensor node are two of the primary concerns. As wireless sensor nodes have been increasingly utilized in smart building applications, the inherent challenge on energy availability leads to prohibitive labor expense and maintenance inconvenience [8].

Table 1. Challenge Factors of a Wireless Sensor Network in Building Management [7]

RankConcern1Lack of installation ease/ease of use2Lack of/concerns about reliability or robustness3Concerns about interference4Lack of standards/interoperability5Power consumption still too high/battery life too short6Overall costs too high7Lacking encryption and other means of security8Bit rate too low/high9Applications not understood/clearly defined10Size of node/endpoints too big

Note that in Fig. 4, the battery pack occupies most of the size and volume of a wireless sensor node. Due to the low energy density of battery material, a battery pack has limited energy capacity. Therefore, the battery energy is depleted in several months and frequent battery replacement is needed. To overcome this severe challenge, energy harvesting wireless sensor node is gaining more and more attention.

Environmental energy sources are ubiquitous in household or industrial surroundings. Such as solar irradiance, thermal gradients, mechanical vibrations, radio frequency waves, etc. Energy harvesting is an energy process of converting ambient energy sources into electrical energy [9,10]. Scavenging environmental energy to extend the operational lifetime of a wireless sensor node is highly appealing. Even though the power density is from hundreds of nanowatts to a few milliwatts, researchers have found that the harvested power is sufficient to sustain a typical wireless sensor [8].

8.4 Radio transceiver modules

8.4.1 BiM-418-F radio transceiver

The BiM-418-F radio transceiver module has two versions, BiM-418-F and BiM-433-F (Radiometrix). The first one operates at 418 MHz frequency band and is type-approved to the Radio Communication Authority in the UK (MPT1340). The latter is for European uses in the 433.92 MHz frequency band. They allow a bi-directional half-duplex data transmission at a speed up to 40 kbyte/s over a distance of 30 metres inside buildings and 120 metres in the open field.

The pin-out is of the BIM-418-F (Radiometrix) shown in Figure 8.11. The working principle of the transmitter and the receiver part of the transceiver are similar to the TMX series radio transmitter and SILRX series receiver modules as described above. Pins 9, 10 and 18 are the ground pins (0 Volts) which are connected to the negative rail of the power supply. Pin 17 is the positive supply pin (Vcc). A DC supply voltage between 4.5 and 5.5V should be connected. When the module is in transmit and receive modes, the current assumption is about 12 mA. When it is in the standby mode, the current reduces to 1 μA. Pin 14 is the transmit data input pin (TXD). It can be driven directly by CMOS logic running on the same supply voltage as the module. Analogue signals generated by modems or DTMF encoders can be also fed into this pin. Pin 12 is the output of the received data. It can be connected directly to CMOS logic. Pin 13 is the output of the analogue signals. It can be used with modems or DTMF decoders. Pin 11 (-CD) is the carrier detect. When the module is in the receive mode, a low state indicates a signal above the detection threshold is being received. Pins 15 (-TX) and 16 (-RX) are used for selecting operation modes of the module.

Figure 8.11. Pin-out of the BiM transceiver

Pin 15=1Pin 16=1standby modePin 15=1Pin 16=0receive modePin 15=0Pin 16=1transmit modePin 15=0Pin 16=0self loop test mode

Pins 1 and 3 are the RF ground. They are internally connected to pins 9, 10 and 18 and should be connected to the ground plane of the user's PCB board against which the antenna radiates. Pin 2 is connected to the antenna. Three types of integral antenna are recommended and approved for use with these modules. The configuration of the antenna and selection chart are given in Figure 8.6.

8.4.2 Requirement for serial data to be transmitted

The data path through a pair of BiMs is AC coupled. Several constraints are placed for a successful data transfer. The pulse with time (i.e. the time between any two consecutive transitions) in the serial code must be within 25 μs and 2 ms. The receiver BiMs require at least 3 ms of 10101010 preamble to be transmitted before the actual data is transferred. The receiver is optimized for data waveforms with 50:50 mark-to-space averaged over any 4 ms period. It will work reliably for sustained asymmetry up to 30/70 either way, but this will result in pulse width distortion and a decreased noise tolerance.

The radio transceiver modules can be used for transmitting RS232 signals between two computers. The experimental circuit is given in Figure 8.12. The RS232 serial data can be transmitted at 4.8 to 38.3 kb/s baud rate between a pair of BiMs. In order to send an RS232 serial data through the BiMs, the data should be packetized in order to meet the requirements by the BiMs. The packetized data includes the following parts: (1) 3 ms of preamble data (55H or AAH) to allow the receiver BiM to settle; (2) 1 or 2 byte of FFH; (3) 1 byte of 01H to show the start of data; (4) data bytes and (5) check bits. In practice, the format of the packetized data may vary according to users’ situations.

Figure 8.12. Experimental circuit diagram of an RS232 radio modem

There are three methods to improve the mark-space ratio of the serial data to be transmitted. The first method is to divide each byte into two. The first half is the bit to be sent and the second half is its compliment. Each byte has a guaranteed mark-to-space ratio of 50:50. Amongst the 256 possible 8-bit codes, 70 codes contain 4 zeros and 4 ones which have a 50:50 mark-to-space ratio. For example, 17H, 1BH, 27H, E8H, etc. They can be transferred between two RS232 ports using an RS232 format of one start bit and one stop bit with no parity check bit. The actual data to be sent will be translated to these codes. This is the second method. For the third method, each byte is sent twice. The first one is the true data and the other is its compliment. This will give 50:50 mark-to-space ratio.

What is an advantage of using radio as an advertising medium quizlet?

Which of the following is an advantage of using radio as an advertising medium? It provides a highly receptive environment to advertisers.

Which of the following is an advantage of radio advertising?

Radio allows messages to be tailored and localized to each targeted audience. Advertisers can direct their message to specific demographics, psychographics, geographic areas, and around events and genres in a market.

Why is radio a poor advertising medium?

Feedback: Radio is heard but not seen, a drawback if the product must be seen to be understood. Some agencies think radio restricts their creative options.

Which of the following would be considered a type of owned media?

Owned media is any web property that you can control and is unique to your brand. One of the most common examples of owned media is a website, although blog sites and social media channels are other examples of owned media properties too.