# Public broadcast satellite utilizing AWS Ground Station Agent (wideband)
This example builds off the analysis done in the [JPSS-1 - Public broadcast satellite (PBS) - Evaluation](examples.md#examples.pbs-definition) section of the user guide.
To complete this example, you'll need to assume a scenario -- you want to capture the HRD communication path as wideband digital intermediate frequency (DigIF) and process it as it's received by the AWS Ground Station Agent on an Amazon EC2 instance using an SDR.
**Note**
The actual JPSS HRD communication path signal has a bandwidth of 30 MHz, but you will configure the *antenna-downlink* config to treat it as a signal with a 100 MHz bandwidth so that it can flow through the correct path to be received by the AWS Ground Station Agent for this example.
## Communication paths
This section represents [Plan your dataflow communication paths](getting-started.step2.md) of getting started. For this example, you will need an additional section in your CloudFormation template that hasn't been used in the other examples, the Mappings section.
**Note**
For more information about the contents of a CloudFormation template, see [ Template sections](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/template-anatomy.html).
You'll begin by setting up a Mappings section in your CloudFormation template for the AWS Ground Station prefix lists by region. This allows the prefix lists to be easily referenced by the Amazon EC2 instance security group. For more information about using a prefix list, see [VPC Configuration with AWS Ground Station Agent](dataflows.vpc-configuration.md#dataflows.vpc-configuration.agent).
```
Mappings:
PrefixListId:
us-east-2:
groundstation: pl-087f83ba4f34e3bea
us-west-2:
groundstation: pl-0cc36273da754ebdc
us-east-1:
groundstation: pl-0e5696d987d033653
eu-central-1:
groundstation: pl-03743f81267c0a85e
sa-east-1:
groundstation: pl-098248765e9effc20
ap-northeast-2:
groundstation: pl-059b3e0b02af70e4d
ap-southeast-1:
groundstation: pl-0d9b804fe014a6a99
ap-southeast-2:
groundstation: pl-08d24302b8c4d2b73
me-south-1:
groundstation: pl-02781422c4c792145
eu-west-1:
groundstation: pl-03fa6b266557b0d4f
eu-north-1:
groundstation: pl-033e44023025215c0
af-south-1:
groundstation: pl-0382d923a9d555425
```
For the Parameters section, you're going to add the following parameters. You'll specify values for these when creating the stack via the CloudFormation console.
```
Parameters:
EC2Key:
Description: The SSH key used to access the EC2 receiver instance. Choose any SSH key if you are not creating an EC2 receiver instance. For instructions on how to create an SSH key see [https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/create-key-pairs.html](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/create-key-pairs.html)
Type: AWS::EC2::KeyPair::KeyName
ConstraintDescription: must be the name of an existing EC2 KeyPair.
AZ:
Description: "The AvailabilityZone that the resources of this stack will be created in. (e.g. us-east-2a)"
Type: AWS::EC2::AvailabilityZone::Name
ReceiverAMI:
Description: The Ground Station Agent AMI ID you want to use. Please note that AMIs are region specific. For instructions on how to retrieve an AMI see [https://docs.aws.amazon.com/ground-station/latest/ug/dataflows.ec2-configuration.html#dataflows.ec2-configuration.amis](https://docs.aws.amazon.com/ground-station/latest/ug/dataflows.ec2-configuration.html#dataflows.ec2-configuration.amis)
Type: AWS::EC2::Image::Id
```
**Note**
You **need** to create a key pair, and provide the name for the Amazon EC2 `EC2Key` parameter. See [ Create a key pair for your Amazon EC2 instance](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/create-key-pairs.html).
Additionally, you'll **need** to provide the correct **region specific** AMI ID, when creating the CloudFormation stack. See [AWS Ground Station Amazon Machine Images (AMIs)](dataflows.ec2-configuration.md#dataflows.ec2-configuration.amis).
The remaining template snippets belong in the Resources section of the CloudFormation template.
```
Resources:
# Resources that you would like to create should be placed within the Resources section.
```
Given our scenario to deliver a single communication path to an Amazon EC2 instance, you know that you'll have a single synchronous delivery path. Per the [Synchronous data delivery](getting-started.step2.md#getting-started.step2.sync-data-delivery) section, you must set up and configure an Amazon EC2 instance with AWS Ground Station Agent, and create one or more dataflow endpoint groups. You'll begin by first setting up the Amazon VPC for the AWS Ground Station Agent.
```
ReceiverVPC:
Type: AWS::EC2::VPC
Properties:
EnableDnsSupport: 'true'
EnableDnsHostnames: 'true'
CidrBlock: 10.0.0.0/16
Tags:
- Key: "Name"
Value: "AWS Ground Station Example - PBS to AWS Ground Station Agent VPC"
- Key: "Description"
Value: "VPC for EC2 instance receiving AWS Ground Station data"
PublicSubnet:
Type: AWS::EC2::Subnet
Properties:
VpcId: !Ref ReceiverVPC
MapPublicIpOnLaunch: 'true'
AvailabilityZone: !Ref AZ
CidrBlock: 10.0.0.0/20
Tags:
- Key: "Name"
Value: "AWS Ground Station Example - PBS to AWS Ground Station Agent Public Subnet"
- Key: "Description"
Value: "Subnet for EC2 instance receiving AWS Ground Station data"
RouteTable:
Type: AWS::EC2::RouteTable
Properties:
VpcId: !Ref ReceiverVPC
Tags:
- Key: Name
Value: AWS Ground Station Example - RouteTable
RouteTableAssociation:
Type: AWS::EC2::SubnetRouteTableAssociation
Properties:
RouteTableId: !Ref RouteTable
SubnetId: !Ref PublicSubnet
Route:
Type: AWS::EC2::Route
DependsOn: InternetGateway
Properties:
RouteTableId: !Ref RouteTable
DestinationCidrBlock: '0.0.0.0/0'
GatewayId: !Ref InternetGateway
InternetGateway:
Type: AWS::EC2::InternetGateway
Properties:
Tags:
- Key: Name
Value: AWS Ground Station Example - Internet Gateway
GatewayAttachment:
Type: AWS::EC2::VPCGatewayAttachment
Properties:
VpcId: !Ref ReceiverVPC
InternetGatewayId: !Ref InternetGateway
```
**Note**
For more information about the VPC configurations supported by the AWS Ground Station Agent, see [AWS Ground Station Agent Requirements - VPC diagrams](https://docs.aws.amazon.com/ground-station/latest/gs-agent-ug/agent-requirements.html#vpc-subnet-diagrams).
Next, you'll set up the Receiver Amazon EC2 instance.
```
# The placement group in which your EC2 instance is placed.
ClusterPlacementGroup:
Type: AWS::EC2::PlacementGroup
Properties:
Strategy: cluster
# This is required for the EIP if the receiver EC2 instance is in a private subnet.
# This ENI must exist in a public subnet, be attached to the receiver and be associated with the EIP.
ReceiverInstanceNetworkInterface:
Type: AWS::EC2::NetworkInterface
Properties:
Description: Floating network interface
GroupSet:
- !Ref InstanceSecurityGroup
SubnetId: !Ref PublicSubnet
# An EIP providing a fixed IP address for AWS Ground Station to connect to. Attach it to the receiver instance created in the stack.
ReceiverInstanceElasticIp:
Type: AWS::EC2::EIP
Properties:
Tags:
- Key: Name
Value: !Join [ "-" , [ "EIP" , !Ref "AWS::StackName" ] ]
# Attach the ENI to the EC2 instance if using a separate public subnet.
# Requires the receiver instance to be in a public subnet (SubnetId should be the id of a public subnet)
ReceiverNetworkInterfaceAttachment:
Type: AWS::EC2::NetworkInterfaceAttachment
Properties:
DeleteOnTermination: false
DeviceIndex: 1
InstanceId: !Ref ReceiverInstance
NetworkInterfaceId: !Ref ReceiverInstanceNetworkInterface
# Associate EIP with the ENI if using a separate public subnet for the ENI.
ReceiverNetworkInterfaceElasticIpAssociation:
Type: AWS::EC2::EIPAssociation
Properties:
AllocationId: !GetAtt [ReceiverInstanceElasticIp, AllocationId]
NetworkInterfaceId: !Ref ReceiverInstanceNetworkInterface
# The EC2 instance that will send/receive data to/from your satellite using AWS Ground Station.
ReceiverInstance:
Type: AWS::EC2::Instance
DependsOn: PublicSubnet
Properties:
DisableApiTermination: false
IamInstanceProfile: !Ref GeneralInstanceProfile
ImageId: !Ref ReceiverAMI
AvailabilityZone: !Ref AZ
InstanceType: c5.24xlarge
KeyName: !Ref EC2Key
Monitoring: true
PlacementGroupName: !Ref ClusterPlacementGroup
SecurityGroupIds:
- Ref: InstanceSecurityGroup
SubnetId: !Ref PublicSubnet
Tags:
- Key: Name
Value: !Join [ "-" , [ "Receiver" , !Ref "AWS::StackName" ] ]
# agentCpuCores list in the AGENT_CONFIG below defines the cores that the AWS Ground Station Agent is allowed to run on. This list can be changed to suit your use-case, however if the agent isn't supplied with enough cores data loss may occur.
UserData:
Fn::Base64:
Fn::Sub:
- |
#!/bin/bash
yum -y update
AGENT_CONFIG_PATH="/opt/aws/groundstation/etc/aws-gs-agent-config.json"
cat << AGENT_CONFIG > "$AGENT_CONFIG_PATH"
{
"capabilities": [
"arn:aws:groundstation:${AWS::Region}:${AWS::AccountId}:dataflow-endpoint-group/${DataflowEndpointGroupId}"
],
"device": {
"privateIps": [
"127.0.0.1"
],
"publicIps": [
"${EIP}"
],
"agentCpuCores": [
24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92
]
}
}
AGENT_CONFIG
systemctl start aws-groundstation-agent
systemctl enable aws-groundstation-agent
#
# Visit the AWS Ground Station Agent Documentation in the User Guide for more details and guidance updates
# Set IRQ affinity with list of CPU cores and Receive Side Scaling mask
# Core list should be the first two cores (and hyperthreads) on each socket
# Mask set to everything currently
# https://github.com/torvalds/linux/blob/v4.11/Documentation/networking/scaling.txt#L80-L96
echo "@reboot sudo /opt/aws/groundstation/bin/set_irq_affinity.sh '0 1 48 49' 'ffffffff,ffffffff,ffffffff' >>/var/log/user-data.log 2>&1" >>/var/spool/cron/root
# Reserving the port range defined in the GS agent ingress address in the Dataflow Endpoint Group so the kernel doesn't steal any of them from the GS agent. These ports are the ports that the GS agent will ingress data
# across, so if the kernel steals one it could cause problems ingressing data onto the instance.
echo net.ipv4.ip_local_reserved_ports="42000-50000" >> /etc/sysctl.conf
#
# We have to reboot for linux kernel settings to apply
shutdown -r now
- DataflowEndpointGroupId: !Ref DataflowEndpointGroup
EIP: !Ref ReceiverInstanceElasticIp
```
```
# The AWS Ground Station Dataflow Endpoint Group that defines the endpoints that AWS Ground
# Station will use to send/receive data to/from your satellite.
DataflowEndpointGroup:
Type: AWS::GroundStation::DataflowEndpointGroup
Properties:
ContactPostPassDurationSeconds: 180
ContactPrePassDurationSeconds: 120
EndpointDetails:
- AwsGroundStationAgentEndpoint:
Name: !Join [ "-" , [ !Ref "AWS::StackName" , "Downlink" ] ] # needs to match DataflowEndpointConfig name
EgressAddress:
SocketAddress:
Name: 127.0.0.1
Port: 55000
IngressAddress:
SocketAddress:
Name: !Ref ReceiverInstanceElasticIp
PortRange:
Minimum: 42000
Maximum: 55000
```
You'll also need the appropriate policies, roles, and profiles to allow AWS Ground Station to create the elastic network interface (ENI) in your account.
```
# The security group for your EC2 instance.
InstanceSecurityGroup:
Type: AWS::EC2::SecurityGroup
Properties:
GroupDescription: AWS Ground Station receiver instance security group.
VpcId: !Ref ReceiverVPC
SecurityGroupEgress:
- CidrIp: 0.0.0.0/0
Description: Allow all outbound traffic by default
IpProtocol: "-1"
SecurityGroupIngress:
# To allow SSH access to the instance, add another rule allowing tcp port 22 from your CidrIp
- IpProtocol: udp
Description: Allow AWS Ground Station Incoming Dataflows
ToPort: 50000
FromPort: 42000
SourcePrefixListId:
Fn::FindInMap:
- PrefixListId
- Ref: AWS::Region
- groundstation
# The EC2 instance assumes this role.
InstanceRole:
Type: AWS::IAM::Role
Properties:
AssumeRolePolicyDocument:
Version: "2012-10-17"
Statement:
- Effect: "Allow"
Principal:
Service:
- "ec2.amazonaws.com"
Action:
- "sts:AssumeRole"
Path: "/"
ManagedPolicyArns:
- arn:aws:iam::aws:policy/AmazonS3ReadOnlyAccess
- arn:aws:iam::aws:policy/service-role/AmazonEC2ContainerServiceforEC2Role
- arn:aws:iam::aws:policy/CloudWatchAgentServerPolicy
- arn:aws:iam::aws:policy/service-role/AmazonEC2RoleforSSM
- arn:aws:iam::aws:policy/AWSGroundStationAgentInstancePolicy
Policies:
- PolicyDocument:
Statement:
- Action:
- sts:AssumeRole
Effect: Allow
Resource: !GetAtt GroundStationKmsKeyRole.Arn
Version: "2012-10-17"
PolicyName: InstanceGroundStationApiAccessPolicy
# The instance profile for your EC2 instance.
GeneralInstanceProfile:
Type: AWS::IAM::InstanceProfile
Properties:
Roles:
- !Ref InstanceRole
# The IAM role that AWS Ground Station will assume to access and use the KMS Key for data delivery
GroundStationKmsKeyRole:
Type: AWS::IAM::Role
Properties:
AssumeRolePolicyDocument:
Statement:
- Action: sts:AssumeRole
Effect: Allow
Principal:
Service:
- groundstation.amazonaws.com
Condition:
StringEquals:
"aws:SourceAccount": !Ref AWS::AccountId
ArnLike:
"aws:SourceArn": !Sub "arn:${AWS::Partition}:groundstation:${AWS::Region}:${AWS::AccountId}:mission-profile/*"
- Action: sts:AssumeRole
Effect: Allow
Principal:
AWS: !Sub "arn:${AWS::Partition}:iam::${AWS::AccountId}:root"
GroundStationKmsKeyAccessPolicy:
Type: AWS::IAM::Policy
Properties:
PolicyDocument:
Statement:
- Action:
- kms:Decrypt
Effect: Allow
Resource: !GetAtt GroundStationDataDeliveryKmsKey.Arn
PolicyName: GroundStationKmsKeyAccessPolicy
Roles:
- Ref: GroundStationKmsKeyRole
GroundStationDataDeliveryKmsKey:
Type: AWS::KMS::Key
Properties:
KeyPolicy:
Statement:
- Action:
- kms:CreateAlias
- kms:Describe*
- kms:Enable*
- kms:List*
- kms:Put*
- kms:Update*
- kms:Revoke*
- kms:Disable*
- kms:Get*
- kms:Delete*
- kms:ScheduleKeyDeletion
- kms:CancelKeyDeletion
- kms:GenerateDataKey
- kms:TagResource
- kms:UntagResource
Effect: Allow
Principal:
AWS: !Sub "arn:${AWS::Partition}:iam::${AWS::AccountId}:root"
Resource: "*"
- Action:
- kms:Decrypt
- kms:GenerateDataKeyWithoutPlaintext
Effect: Allow
Principal:
AWS: !GetAtt GroundStationKmsKeyRole.Arn
Resource: "*"
Condition:
StringEquals:
"kms:EncryptionContext:sourceAccount": !Ref AWS::AccountId
ArnLike:
"kms:EncryptionContext:sourceArn": !Sub "arn:${AWS::Partition}:groundstation:${AWS::Region}:${AWS::AccountId}:mission-profile/*"
- Action:
- kms:CreateGrant
Effect: Allow
Principal:
AWS: !Sub "arn:${AWS::Partition}:iam::${AWS::AccountId}:root"
Resource: "*"
Condition:
ForAllValues:StringEquals:
"kms:GrantOperations":
- Decrypt
- GenerateDataKeyWithoutPlaintext
"kms:EncryptionContextKeys":
- sourceArn
- sourceAccount
ArnLike:
"kms:EncryptionContext:sourceArn": !Sub "arn:${AWS::Partition}:groundstation:${AWS::Region}:${AWS::AccountId}:mission-profile/*"
StringEquals:
"kms:EncryptionContext:sourceAccount": !Ref AWS::AccountId
Version: "2012-10-17"
EnableKeyRotation: true
```
## AWS Ground Station configs
This section represents [Create configs](getting-started.step3.md) of getting started.
You'll need a *tracking-config* to set your preference on using autotrack. Selecting *PREFERRED* as autotrack can improve the signal quality, but it isn't required to meet the signal quality due to sufficient JPSS-1 ephemeris quality.
```
TrackingConfig:
Type: AWS::GroundStation::Config
Properties:
Name: "JPSS Tracking Config"
ConfigData:
TrackingConfig:
Autotrack: "PREFERRED"
```
Based on the communication path, you'll need to define an *antenna-downlink* config to represent the satellite portion, as well as a *dataflow-endpoint* config to refer to the dataflow endpoint group that defines the endpoint details.
```
# The AWS Ground Station Antenna Downlink Config that defines the frequency spectrum used to
# downlink data from your satellite.
SnppJpssDownlinkDigIfAntennaConfig:
Type: AWS::GroundStation::Config
Properties:
Name: "SNPP JPSS Downlink WBDigIF Antenna Config"
ConfigData:
AntennaDownlinkConfig:
SpectrumConfig:
Bandwidth:
Units: "MHz"
Value: 100
CenterFrequency:
Units: "MHz"
Value: 7812
Polarization: "RIGHT_HAND"
# The AWS Ground Station Dataflow Endpoint Config that defines the endpoint used to downlink data
# from your satellite.
DownlinkDigIfEndpointConfig:
Type: AWS::GroundStation::Config
Properties:
Name: "Aqua SNPP JPSS Terra Downlink DigIF Endpoint Config"
ConfigData:
DataflowEndpointConfig:
DataflowEndpointName: !Join [ "-" , [ !Ref "AWS::StackName" , "Downlink" ] ]
DataflowEndpointRegion: !Ref AWS::Region
```
## AWS Ground Station mission profile
This section represents [Create mission profile](getting-started.step4.md) of getting started.
Now that you have the associated configs, you can use them to construct the dataflow. You'll use the defaults for the remaining parameters.
```
# The AWS Ground Station Mission Profile that groups the above configurations to define how to
# uplink and downlink data to your satellite.
SnppJpssMissionProfile:
Type: AWS::GroundStation::MissionProfile
Properties:
Name: !Sub 'JPSS WBDigIF gs-agent EC2 Delivery'
ContactPrePassDurationSeconds: 120
ContactPostPassDurationSeconds: 120
MinimumViableContactDurationSeconds: 180
TrackingConfigArn: !Ref TrackingConfig
DataflowEdges:
- Source: !Ref SnppJpssDownlinkDigIfAntennaConfig
Destination: !Ref DownlinkDigIfEndpointConfig
StreamsKmsKey:
KmsKeyArn: !GetAtt GroundStationDataDeliveryKmsKey.Arn
StreamsKmsRole: !GetAtt GroundStationKmsKeyRole.Arn
```
## Putting it together
With the above resources, you now have the ability to schedule JPSS-1 contacts for synchronous data delivery from any of your onboarded AWS Ground Station [AWS Ground Station Locations](aws-ground-station-antenna-locations.md).
The following is a complete CloudFormation template that includes all resources described in this section combined into a single template that can be directly used in CloudFormation.
The CloudFormation template named `DirectBroadcastSatelliteWbDigIfEc2DataDelivery.yml` is designed to give you quick access to start receiving digitized intermediate frequency (DigIF) data for the Aqua, SNPP, JPSS-1/NOAA-20, and Terra satellites. It contains an Amazon EC2 instance and the required CloudFormation resources to receive raw DigIF direct broadcast data using AWS Ground Station Agent.
If Aqua, SNPP, JPSS-1/NOAA-20, and Terra are not onboarded to your account, see [Onboard satellite](getting-started.step1.md).
**Note**
You can access the template by accessing the customer onboarding Amazon S3 bucket using valid AWS credentials. The links below use a regional Amazon S3 bucket. Change the `us-west-2` region code to represent the corresponding region of which you want to create the CloudFormation stack in.
Additionally, the following instructions use YAML. However, the templates are available in both YAML and JSON format. To use JSON, replace the `.yml` file extension with `.json` when downloading the template.
To download the template using AWS CLI, use the following command:
```
aws s3 cp s3://groundstation-cloudformation-templates-us-west-2/agent/ec2_delivery/DirectBroadcastSatelliteWbDigIfEc2DataDelivery.yml .
```
You can view and download the template in the console by navigating to the following URL in your browser:
```
https://s3.console.aws.amazon.com/s3/object/groundstation-cloudformation-templates-us-west-2/agent/ec2_delivery/DirectBroadcastSatelliteWbDigIfEc2DataDelivery.yml
```
You can specify the template directly in CloudFormation using the following link:
```
https://groundstation-cloudformation-templates-us-west-2.s3.us-west-2.amazonaws.com/agent/ec2_delivery/DirectBroadcastSatelliteWbDigIfEc2DataDelivery.yml
```
**What additional resources does the template define?**
The `DirectBroadcastSatelliteWbDigIfEc2DataDelivery` template includes the following additional resources:
+ **Receiver Instance Elastic Network Interface** - (Conditional) An elastic network interface is created in the subnet specified by **PublicSubnetId ** if provided. This is required if the receiver instance is in a private subnet. The elastic network interface will be associated with the EIP and attached to the receiver instance.
+ **Receiver Instance Elastic IP** - An elastic IP that AWS Ground Station will connect to. This attaches to the receiver instance or elastic network interface.
+ One of the following Elastic IP associations:
+ **Receiver Instance to Elastic IP Association** - The association of the Elastic IP to your receiver instance, if **PublicSubnetId ** is not specified. This requires that **SubnetId ** reference a public subnet.
+ **Receiver Instance Elastic Network Interface to Elastic IP Association ** - The association of the elastic IP to the receiver instance elastic network interface, if **PublicSubnetId** is specified.
+ (Optional) **CloudWatch Event Triggers** - AWS Lambda Function that is triggered using CloudWatch Events sent by AWS Ground Station before and after a contact. The AWS Lambda Function will start and optionally stop your Receiver Instance.
+ (Optional) **Amazon EC2 Verification for Contacts** - The option to use Lambda to set up a verification system of your Amazon EC2 instance(s) for contacts with SNS notification. It is important to note that this may incur charges depending on your current usage.
+ **Additional mission profiles** - Mission profiles for additional public broadcast satellites (Aqua, SNPP, and Terra).
+ **Additional antenna-downlink configs** - Antenna downlink configs for additional public broadcast satellites (Aqua, SNPP, and Terra).
The values and parameters for the satellites in this template are already populated. These parameters make it easy for you to use AWS Ground Station immediately with these satellites. You do not need to configure your own values in order to use AWS Ground Station when using this template. However, you can customize the values to make the template work for your use case.
**Where do I receive my data?**
The dataflow endpoint group is set up to use the receiver instance network interface that part of the template creates. The receiver instance uses the AWS Ground Station Agent to receive the data stream from AWS Ground Station on the port defined by the dataflow endpoint. For more information about setting up a dataflow endpoint group, see [ AWS::GroundStation::DataflowEndpointGroup](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-groundstation-dataflowendpointgroup.html). For more information about the AWS Ground Station Agent, see [ What is the AWS Ground Station Agent? ](https://docs.aws.amazon.com/ground-station/latest/gs-agent-ug/overview.html)